In the summer, you can ride or hike for days through spruce forests and across snow-chilled streams and see barely a soul. In the winter, you might share Pioneer Mountain with just a handful of other skiers. For the more clubbable, a hillside golf course offers spectacular views, while fine wining and dining is always close at hand.

This is the über-exclusive Yellowstone Club, 13,000 acres under the "big sky" of Montana, a retreat where the super-rich can relax, spend time with their families, or entertain. The entry fee is $250,000 (£130,000), though you'll have to be invited and you'll have to buy a house (the developers are currently building the world's most expensive, a $155m mansion that has environmental campaigners up in arms) in order to gain acceptance. It is rumoured that the members - of whom there are fewer than 300 - include Bill Gates, the Microsoft founder turned global philanthropist-in-chief, the former US Vice-President Dan Quayle and stars including Brad Pitt. There are also a smattering of trust-fund consumers, Wall Street titans past and present, and numerous serving chief executives, bloated on corporate America's generous boardroom pay.

Pity them, they need help. A fortune can be a terrible burden when it must be protected, invested and sheltered from the tax man, parcelled out ready for future generations. Even giving it away is not easy, requiring all sorts of expertise to navigate the world of philanthropy and competing demands for donations and sponsorships. So step forward - or more accurately in some cases, ski forward - the private wealth manager.

Clever, discreet, urbane, the private wealth manager is a banker-cum-broker-cum-butler to the super-rich. He or she will be trusted with the family's financial secrets, relied upon to advise and to manage its financial needs, perhaps also, in a spare moment, to pick up an impossible-to-find box at a sports game or to deal with a pesky bill that has been overlooked.

It is in rarified worlds such as Yellowstone that these advisers can most easily ski, golf and dine their way into the lives of the people that the industry likes to call "ultra-high net worth individuals". It's a trade in which you have got to spend money to make monied individuals come to you.

This is not because they are impressed by the trappings of wealth per se, says Russ Prince, the founder of Prince & Associates, a consultancy that studies the habits of the super-rich. Rather, it is what that wealth signifies. "This is all about money," said Prince. "If you want to deal with the super-rich, it is important to have some measure of success of your own. A man in a mansion is not going to take advice from a man who lives in a hovel."

America's modern super-rich exist at the intersection of business and philanthropy and art and politics, so those who seek to advise them must hover there too. For the vain, for the greedy and for the bedazzled, it can be a terrible trap.

It is at this intersection that Wall Street is enjoying its first great scandal of 2007 (there will surely be others - this is boom-time for the finance industry) and it is for this reason that private wealth managers are facing more scrutiny than ever before. Just how far will they go, how far should they go, to woo their clients? And what happens when they start to enjoy the life a little too much?

Todd Thomson did not live or work in a hovel. At 45, Thomson was one of the finance industry's fastest-rising stars, and was heading the wealth management division of the banking giant Citigroup, which acts for hundreds of the richest individuals and families in America, making him one of the most powerful advisers of the super-rich.

His holiday home at the Yellowstone Club became a favoured venue for skiing parties for clients - and those he hoped would soon become clients. But Yellowstone was not his only indulgence. Far from it. When he was suddenly fired at the start of this year, what was revealed about his free-spending way with Citigroup's corporate credit card provoked shock and awe in equal measure. News that the beneficiary of much of his corporate largesse was one of America's most telegenic business reporters turned the usually austere front page of The Wall Street Journal into something akin to a celebrity gossip rag.

Thomson's attempts to impress his Yellowstone counterparts and other potential clients, had extended to a costly make-over for his 50th-floor office back in New York, where the views of Central Park were not apparently enough of a draw. The floor's boardroom, almost exclusively used by Thomson, is decked out with marble flooring and polished wood cabinets; in his main office was installed a tropical fish tank and Persian rugs and, in an expense too far, a giant wood-burning fireplace. Visitors have compared it to a "Swiss chalet" or the inner sanctum of the Wizard of Oz; Citigroup insiders dubbed it the "Todd Mahal".

The gossips of Wall Street (that is, everyone on Wall Street) have thoroughly enjoyed the innuendo surrounding the relationship between Thomson and Maria Bartiromo, dubbed "the Money Honey" for her reporting from the New York Stock Exchange floor. They have nudged at the time Thomson kicked other executives off the corporate jet to fly solo with Bartiromo, and winked at a sighting of the two dining together at the exclusive Upper East Side restaurant Daniel. But an infuriated Bartiromo, flanked by her husband Jonathan Steinberg at the outlandish birthday party for private equity bigwig Stephen Schwarzman this month, was telling friends that she was despairing of her profession after seeing so many inaccuracies in print. Bartiromo says she was cultivating a damn good source; Thomson says that Bartiromo simply added a sprinkle of celebrity that impressed potential clients on marketing trips in Asia.

The Citigroup board decided his expenditures on the office and on the reporter constituted lapses of judgment; Wall Street and its commentariat has tended to agree. The poison is barely dry on the profiles of Thomson, but there is a respectable revisionist theory - that his expenditures were just part of the job and they may even have been good value for money.

Thomson may well be right to insist that the fireplace provided a conducive backdrop to host "fireside chats" for clients with guests such as Citigroup's erstwhile chairman and CEO, the fêted Sandy Weill. These intangible slivers of access to the powerful, the famous and the clever may not impress the super-rich exactly, but they cultivate the impression of "having connections".

Russ Prince says that contacts and connections are vital, and that moving in the right circles and giving the right impression can be a more surefire way of securing lucrative business than any other. "I know of one successful adviser who was in a car accident with a wealthy gentleman who subsequently became his client. It is, of course, not sensible to go running your car into Bentleys. It is costly, and you may only get the chauffeur."

There is more wealth around to be advised. On Wall Street, bankers in the top echelons of hot fields like mergers or derivatives trading have taken home multimillion dollar pay packets for at least three years in a row. The hedge fund industry is burgeoning, creating a new set of super-rich businesspeople. In Britain, City bonuses are at record highs and new money mingles with old. Overseas, economic expansion in India and the Far East has turned struggling entrepreneurs into instant lottery winners. It is no surprise, therefore, that competition is fierce among the advisers to the super-rich.

And with private wealth managers typically taking a small annual percentage of the fortune on which they advise, the fees can stack up to a more than comfortable living. The top independent advisers typically take home more than $5m a year from perhaps just a handful of clients, and many take home double that. Those who operate inside much bigger financial institutions are lavished with bonuses that can break the million-dollar mark because of the profits they can generate. Some of the most influential advisers are fought over by institutions desperate for access to their Rolodexes; Anthony DeChellis, for example, hopped from Merrill Lynch to UBS to Credit Suisse in the space of three years.

John Straus, head of private wealth management at the Swiss banking giant UBS, said: "When you become the 'trusted adviser', it becomes a very close relationship. Advisers are often invited to weddings and to birthday celebrations - after all, they are familiar with many things about a family that are not widely known and there has to be same level of comfort as a friendship. Obviously, clients don't like turnover, so it is important that our best people feel good, feel valued and don't leave the firm."

Relationships between advisers and their clients can last many years; often not even age can wither them. Goldman Sachs, at a jamboree for its advisers in Scottsdale, Arizona, has just honoured Al Feld, who is entering his 75th - yes, 75th - year with the firm. Gary Giglio, head of global private wealth management development at Goldman Sachs, says: "The great news about this business is that it is so dynamic and so broad, and is continually growing and evolving, that you can have a long and fulfilling career."

Advisers will use all their club memberships and connections to put on events that attract clients, whether it be informal getaways such as the "women's retreat" organised annually by the Palm Beach, Florida advisers company AMA, or formal investment seminars (with a slap-up meal, of course) such as that arranged recently by the lawyers Withers Bergman in the plush environs of the Indian Harbor Yacht Club, Greenwich, in the heart of the "hedge fund belt" in Connecticut.

And the office must be impressive, too. Across town from the Todd Mahal, UBS has just opened a "pilot office" that brings all its local advisers and other financial experts together in a single location designed to wow super-rich clients. It has already been deemed a success and will be copied in other cities where UBS seeks ultra-high net worth clients, those whose fortunes extend to nine figures or more.

The Swiss bank has gone for a different, more modern - some would say more tasteful - aesthetic to that chosen by Todd Thomson, but it reeks just as strongly of money and power. The fully catered dining and meeting rooms offer spectacular views up through the valleys and glaciers of Manhattan's Midtown skyscraper district; in the lobby hangs a vibrant piece by the contemporary American painter Jasper Johns, whose works have started disappearing into the private collections of hedge fund managers for sums up to $80m.

Amid it all, the silver-haired boss, John Straus, is remarkably unassuming, with a pen pointing out of the breast pocket of a plain white shirt, but he is no less charming than you would expect. The finest advisers at UBS, he says, must be urbane and erudite on subjects ranging from esoteric investments in the derivatives markets to the merits of classic cars, watches, wines, antiques and, of course, art.

UBS sponsored December's Art Basel art fair in Miami Beach, an expenditure that allowed it to offer its wealthy clients special access to artist presentations and the opportunity to mingle with dealers. Straus said: "Art is something that many people are very passionate about. We have clients who are captains of their industries, but are always also thinking about and talking about art and they direct the same amount of energy into their art collection. My own passion is cars, commercial rather than classic cars. My dream client is one who will take me down to the basement to see his 200-car collection."

Straus's vehicle collection is not likely to reach such proportions. Though the best advisers can end up becoming multimillionaires, the super-rich are accelerating away from other humans. In 2006, for the first time, to get on the Fortune 400 list of the richest Americans, a person had to be a certified billionaire.

The irony is that the fallen Thomson was on the cusp of becoming one of the super-rich that he was sacked for mimicking. He was one of two executives battling to take over from the current Citigroup chief executive, Chuck Prince, a promotion which would have given him the keys to the cash tin marked "Wall Street excess". His conspicuous expenditure came, though, at an unfortunate time, since shareholders - who include the world's eighth-richest man, Saudi prince Alwaleed Bin Talal (estimated net worth, $20bn) - have been arguing that costs across the group have spun out of control. An old-timer with a reputation for ruthless cost-cutting was promoted above his head, and suddenly Thomson is "looking forward to new challenges".

Many of the wealth management industry's most colourful characters have always been known for their conspicuous spending. Art Bavelas, founder of Resource Network, "makes Paris Hilton look like an old maid", according to one associate who has been regaled by stories of his chartering private jets to go on shopping trips. Others gain a higher profile when enthusiastic clients hold open doors to corporate America. Maria Lagomasino, chief executive of AMA, who fled Castro's revolution with her family as a child, has networked her way to the top and is now a regular on company boards that have included Avon and Coca-Cola. Her prominence in part comes from having cheerleading clients such as Gary Winnick, former head of the brokerage firm Global Crossing, who asked her to join his ill-fated telecoms company's board in 2001.

Others still are rich and famous in their own right as scions of established dynasties. Many such families have long maintained an office that looks after their financial affairs, accumulating plenty of their own expertise and seeking outside help only for specific, limited transactions. The most revered of all such "family offices" is that of the Rockefeller family, which still runs the great fortune out of Room 5600 on the 56th floor of the Rockefeller Center, from whence used to come investment decisions that could cause a minor tremor on Wall Street.

Inside these family offices as the generations pass, the fortune fragments, the paperwork and the decision-making process - not to mention the intra-family rivalries - become ever more fraught and the costs of maintaining the office escalate, sometimes to the point where they are gobbling up the fortune. In this scenario the most sensible thing to do is to team up with other families, seek economies of scale and share out some of the wealth management expertise learned over the decades. This is why Abby O'Neill, eldest grandchild of John D Rockefeller Jr, has been in recent years not just matriarch of the great philanthropic dynasty, not just a patron of the arts and education, but also sometime head of Rockefeller & Co, the wealth management business run out of Room 5600. Don't expect the Rockefellers to go touting for business on the cocktail party circuit, though. The company's website is designed to repel. "We are a boutique firm that caters to a select clientele," it thunders, demanding more information from potential clients before it hands out further details.

Other "multi-family offices" have grown to the point that they are now significant wealth managers in their own right. With its fortuitous position within the necklace of golf courses that make Florida's coast a winter playground for the rich, AMA has grown out of the personal office of the Perry family, based on the local newspaper and cable industry fortune of John Perry and then his son, John Jr, an inventor and undersea explorer who reputedly taught the Duchess of Windsor to twist. Hap Perry, John Jr's son, is still AMA chairman.

And in the other corner of the US, under a street-level park with reflecting pools and waterfalls, in an eye-catching eco-friendly building designed and built from scratch, the septuagenarian multimillionaire George Russell is building a second giant business. Having made a first fortune from the Frank Russell pension advisory business, which he sold for $1bn in 1998, his new Threshold Group is one of the fastest growing "multi-family offices", taking on just the sort of urbane and erudite advisers who can win clients over from brand-name institutions like Citigroup. There is a world of difference between the solicitous fireside chats on Wall Street and the marketing preferred by Russell, who counts Secretary of State Condoleezza Rice and imprisoned Russian tycoon Mikhail Khordorkovsky among his friends. At Threshold, potential clients must be able to rub together at least $100m, and it is they who have to be solicitous if they are to get in the door. "We've turned down a couple," Russell sniffed in an interview last year. "Their value system was different from ours."

And there's the difficulty. The already-monied families easily share the values of their potential clients. Wall Street arrivistes such as Citigroup and Thomson, well, they're just faking it.

In the end, it is not just reasonable but necessary that these wealth managers partake in the perks of the job - they must just take care not to get carried away. "You'll get time on a 300ft yacht; you'll have lunch with a billionaire. It gives you access to a lifestyle that you normally wouldn't be able to afford," says Russ Prince. "Advisers' houses are substantial, but they are not going to top their clients'. The smart ones say 'OK, I didn't inherit $500m, I'm not going to make $1bn', and then they get over it. Advisers are not buying private islands but, yes, they are buying jets. They are going to make a few million dollars - it ain't bad."

In the club: where business meets pleasure

By Guy Adams

Yellowstone Club

What The highest-end "destination club" in the world, it's a private holiday resort set in 13,400 acres of countryside in the Montana mountains. By winter, Yellowstone is a powder skiier's paradise; by summer, there's a Tom Weiskopf-designed golf course, together with some highly regarded riding, walking and fly-fishing.

Who Fewer than 300 members, recruited on an invitation-only basis. Their identities are a closely guarded secret, though regulars are rumoured to include Bill Gates, Dan Quayle, and Brad Pitt.

How much Entry fee of $250,000 (£130,000), plus annual subscriptions of around $10,000. And you'll need to buy a house within the resort at somewhere between $2m and $155m.

Bath and Tennis Club

What Palm Beach in Florida is the number one holiday resort for America's rich and powerful. The Bath and Tennis is its most exclusive country club. It was built by the architect Addison Mizner for Gatsby generation of the 1920s, and sits on several hundred prime acres off Ocean Boulevard.

Who Anyone who's anyone in American Society. Brits to have been welcomed range from the Duke and Duchess of Windsor to the current Duke of Marlborough and Prince and Princess Michael of Kent.

How much Top secret. And if you have to so much as ask, you've no chance of getting in. For a ball-park figure, it's worth noting that at Donald Trump's Mar-a-Lago club next door, membership costs a cool $250,000.

Indian Harbor Yacht

What The poshest "yotties" retreat on the East Coast, it was founded in 1889 to organise regattas for weekending New Yorkers. Runs serious racing teams, coaches the offspring of the super-rich and, away from the water, organises cocktail parties and conferences for white-collar networkers.

Who Connecticut is spiritual home to the hedge fund billionaire. The club's Commodore, Peter J Cummiskey, and Vice Commodore, Samuel B Fortenbaugh III all made fortunes on Wall Street before deciding to spend more time with their yachts.

How much A relatively modest $10,000 a year, with about the same again in joining fees. But only if you can become a member - and the waiting list is more than 15 years long.