It's easy to lose touch with reality when you're top of the world, ma. And JK Rowling's extraordinary rise from income support and single parenthood to the upper reaches of the Sunday Times' Rich List makes her a prime candidate for the Icarus Syndrome: that is, losing the plot then coming a cropper.

The unending adulation, the incessant sycophancy, the perpetual publicity, the fountain of royalties, the litany of literary awards, the non-stop Harry Potter chatter - and all that goes with it - would turn almost anyone's head, even someone as level-headed as Joanne Rowling appears to be.

She's aware of this possibility, of course. Rowling worries that hubris will befall her, as it has befallen many other celebrities in similarly sequestered circumstances. Martha Stewart, Britney Spears, Chris Evans, George Michael, Michael Jackson, Naomi Campbell, Conrad Black, Courtney Love, John Browne, Paris Hilton, Tony Blair and more besides have flown too close to the sun on occasion. And came crashing down like Icarus as a consequence.

The questions remain, however. Has Rowling avoided high flyers' foremost occupational hazard? Is she a victim of the 'reality distortion field' that famously afflicts Steve Jobs, Apple Inc's iconic CEO, who crashed and burned in the mid-1980s? Are we dealing with a classic case of do-as-I-say-not-as-I-do? Let the jury decide ...

Earlier this year, Rowling urged readers to support their local bookshops and resist the price-cutting chain stores and supermarkets. Yet it is supermarkets' fearsome discounting on the Harry Potter series that has done much to shift the balance of bookselling power from independent retailers to chain stores.

Discounting is so ferocious on the Harry Potter books that independents can't make money from the teenage wizard and some are refusing to stock the seventh volume. The supermarkets, conversely, having established their bookselling credentials with Harry Potter loss-leaders are, grabbing more and more market share. In such circumstances, Rowling's 'shop local' recommendations ring rather hollow, to put it mildly.

On another recent occasion, Rowling lambasted the fashion glossies for their fixation with stick-thin, size-zero models, which gives rise to body image anxiety among impressionable adolescents. But Rowling herself hasn't been averse to a bit of body image exploitation. The revolting corpulence of Dudley Dursley is mocked on numerous occasions in the early books, as is the obscene obesity of Dudley's dad, Vernon, and his unspeakable Aunt Marge. Bearing in mind that the Potter books are targeted at impressionable adolescents, Joanne's relentlessly negative portrayal of the overweight doesn't do her any credit.

Indeed, it could be argued that the Harry Potter books have contributed to the obesity outbreak that Rowling takes comic advantage of. By my reckoning, the pupils at Hogwarts eat eight to 10 multi-course meals per day. They often have seconds. In between meals, they're constantly stuffing their faces with sugary snacks like Chocolate Frogs and Cockroach Clusters, to say nothing of fizzy, pumpkin-flavoured beverages. This is not a good example to be setting our children. Something must be done! Where's Jamie Oliver when you need him?

Body image and bookselling aside, there's another aspect of the Harry Potter phenomenon that simply screams Icarus. Marketing. Rowling has repeatedly railed against the commercialisation of her series. Yet she is no slouch when it comes to cranking the marketing machine.

In July 2006, she let it slip that Harry Potter might not survive the final volume. Cue acres of newspaper coverage and copious free publicity. Funnily enough, her announcement just happened to coincide with the release of the paperback edition of Half-Blood Prince. Strange that.

Likewise, Rowling's decision to restrict her personal appearances during recent book release campaigns is a masterstroke of marketplace manipulation. It's exactly the same 'denial marketing' strategy that drives Topshop, Primark and H&M's customers wild with gotta-have-it desire. By restricting her appearances to a very limited group of media representatives - as per the Edinburgh Castle event in 2005 - Rowling drives producers, editors and columnists wild with gotta-cover-it desire. For all her anti-marketing rhetoric, JKR is an authorpreneur of the first rank.

Some, of course, might conclude that Rowling's restricted entry, quasi-royal audiences in Edinburgh Castle are proof positive that she's finally lost the plot. Maybe the 'Queen of Teen Fiction' appellation has gone to her head. Perhaps the oft-reported fact that she outranks Her Majesty the Queen on the Sunday Times Rich List has clouded Jo's judgement. Then again, it could be she's suffering from an entirely understandable case of humility fatigue. Her recent defacement of a statue in the Balmoral Hotel, which was inscribed with a proclamation that she'd finished writing Deathly Hallows on the premises, speaks volumes in that regard. Most of us would end up in court if we chose to scribble on the five-star hotel's statuary. Different rules presumably apply at the court of the Sun Queen, HRH JKR.

Rowling, in fairness, always comes across as someone who remains refreshingly down to earth, despite the hype, the hoopla, the hubris-enriched hot air that surrounds her.

Her Icarus quotient, one suspects, is much lower than many others in her otherworldly circumstances. Her altruism is much admired. Her achievements are incomparable. Her literary legacy is assured. Her wax wings are dripping, though.

Stephen Brown has published a book called Wizard! Harry Potter's Brand Magic, Cyan, £7.99. His new book Fail Better! a study of success and failure in business will be published by Cyan in August

Harry Potter And The Deathly Hallows is due out in July