Room 652 in the Balmoral Hotel, Edinburgh, is a place which most people, save the lucky few who can afford the £300-a-night room fee, could expect to know little about.

Until yesterday, that is. We now know, for example, that the room comes adorned with a marble bust, that it was the chosen site for JK Rowling to pen the final instalment of her latest novel and that, on January 11, she wrote the last sentence in the last chapter of what is already the biggest publishing phenomenon in history.

It is testament to the juggernaut of hype, publicity, cult following and genuine excitement of millions of fans around the world that this room - already dubbed the "Harry Potter Suite" by some - is destined to become another shrine to Rowling's famous creation - an ordinary, muggle landmark touched upon by the magic of the boy wizard's world.

Already, platform 93/4 at Kings Cross Station, the departure point of the Hogwarts Express, has been officially marked for passing tourists. Alnwick Castle, the location used in the film spin-offs as a stand-in for the boarding school, and the Glenfinnan Viaduct, which the express famously crosses, have become known to thousands of visitors as much for their movie connotations as their picturesque beauty.

The books have certainly transformed Rowling. From her humble beginnings in a mouse-infested Edinburgh flat, she is now thought to be the second richest woman in the world - after Oprah Winfrey - with a wealth estimated at around £507m, according to Forbes magazine. Indeed, she is thought to be the only person to become a billionaire (admittedly in dollar terms) through writing.

If anyone is attuned to the sometimes surreal, fever-pitch excitement that surrounds these magical creations, it is surely Rowling herself. In what friends say is a typically humorous gesture, she marked the end of Harry Potter and the Deathly Hallows, the final instalment in the series, by scribbling on said bust: "JK Rowling finished writing Harry Potter + the Deathly Hallows in this room (652) on 11th Jan 2007."

Possibly influenced by the fame of its guest and the tourism appeal of the newly decorated bust, the Balmoral took an unusually tolerant view towards the vandalism.

"Obviously this is a unique case," hotel spokeswoman Jessica Trotter said yesterday. "We're honoured and flattered she chose the Balmoral as surroundings to do her writing."

The setting where Rowling penned the last of the Harry Potter series is a far cry from the Edinburgh cafes - The Elephant House and Nicholson's coffee shop - where she famously began the first of them 10 years ago as a single mother living on benefits. Then, she struggled to find an agent and was turned down by eight publishers. A decade later, she has been credited with transforming the publishing world and changing our definition of what a children's novel can be.

Julie Bertagna, the Scottish children's author who had her first novel published around the same time as The Philosopher's Stone, said the effect had been amazing. "It's the equivalent of the Beatles in children's publishing. My feeling is that we should be proud of her in Scotland," she said.

"Ten years ago, children's fiction was a stagnant backwater which nobody really took very seriously at all. In the last 10 years there's been a revolution which is mostly due to Harry Potter."

The result of this revolution, Bertagna believes, is that the genre is now taken seriously by readers and publishers alike. "In publishing houses, money men now take children's books seriously because they can make money. The downside is that a lot of books that maybe don't deserve it get hyped, especially books written by celebrities," she adds.

As well as transforming expectations of publishing, the books have also left an indelible mark on the imaginations of millions of children and adults around the world: the rules of Quidditch, the history of Hogwarts and the childhood tragedies of Harry have become as familiar to us now as the fantastical world of Alice or the hermetically sealed universe of JRR Tolkien. For a generation of youngsters, Harry's rites of passage have mirrored theirs; he has grown as they have.

Keith Gray, an Edinburgh-based children's author, counts himself as a fan. "The books have caused a splash and a lot of children out there have felt the ripples. I just think the world is so well-imagined. It's in the detail of that world. It's very well drawn," he says.

But the books have not been short of detractors. Julian Baggini, founding editor of The Philosophers' Magazine who has written previously about the philosophy of The Simpsons, called them an "infantile indulgence".

Stressing he has no beef with children reading the books, he takes umbrage at their burgeoning adult audience whom, he says, are attracted by the comforting escapism they offer.

" I've come to the conclusion that adults like them precisely because they're very childish and they can deliberately immerse themselves in that world," he says. "They have a sense of familiarity: although each book has a new story, everything in it has echoes of classical storylines - the orphan, the fight between good and evil. It offers an escape from adult worries. It's like Angel Delight. When a child eats it, they are eating it for the first time and enjoy its taste. But for an adult, part of the enjoyment is in the sense of nostalgia."

Some of the criticism, Bertagna feels, has been inevitable, given the size and momentum of the Harry Potter publishing empire. "You could look at any book in the world and say it's not worthy of that level of hype," she says. "But you can pick apart any book. The important thing is they've got millions of children reading and millions of boys reading, which is a hard thing to do. How can you knock that?"

The books also have a string of defenders who vouch for more than their page-turning qualities. Richard Woolfson, a child psychologist, believes Rowling is that rare thing in an author: someone who can connect with children on their own turf and using their own language - a quality shared with Roald Dahl.

For children struggling with, as one child psychiatrist famously put it, "the drama of childhood", Harry Potter's travails present an opportunity to confront issues - big issues - they might otherwise find it difficult to discuss, he says.

"She deals with evil in a child-centric way. There are dark characters who are dark because, essentially, they are bullies and unpleasant. Children do have bullies and unpleasantness in their lives and can map the characters they know onto the characters in Rowling's books. They're authentic."

Dr Karen McGavock, a researcher at Dundee University whose PhD thesis examined Harry Potter and the Order of the Phoenix, believes the books are valuable for more than saving the "Nintendo generation" from a childhood of stupefied computer game addiction. She is fascinated by Rowling's exploration of childhood and adulthood and what she sees as a blurring of the boundaries between them.

"Whereas, in the works of JM Barry, CS Lewis and Lewis Carroll, you have an idealised, sentimentalised version of childhood, Rowling is undermining and deconstructing this. They depart from her predecessors in that way," she says. "The books explore the boundaries between childhood and adulthood, which are more blurred than they have appeared in previous children's literature. Rowling is doing something new in that respect."

In dementors, the foreboding wraiths which darken Harry's days at Hogwarts, McGavock sees an exploration of depression and the darker side of the human character. Killing Harry off - a plot twist which has been widely speculated upon - would represent "a 21st-century version of the death of childhood" she claims.

For the millions of readers who have taken Harry into their hearts, his death - even his fictional retirement - will not be so symbolic. It will simply be the loss of a dear friend.