Is there any evidence supporting or contradicting the theory that Harry is an abused child, imagining it all?

In the article Why Hogwarts Was All in Harry's Head: A Conspiracy Theory on Cracked.com ^{(WARNING: time sink)}, it is proposed that Harry Potter is imagining eveything – being a wizard, Hogwarts, Hermione, Ron, and Voldemort – escaping into a fantasy world as a coping mechanism for the child abuse he receives. I think I've read the same theory elsewhere as well, but I'm not sure.

I find this an interesting idea. Is there anything in canon that either supports or contradicts this theory? Please note that I'm not merely asking for your opinion if it was all just a dream ^{(WARNING: time sink)}; I understand that the same argument can be made about pretty much any story. I'm asking for evidence regarding this specific theory.
What I'm looking for, is anything in canon or anything said or written by the author, that either gives credence to the theory, like "that dovetails nicely with X, Y, and Z", or that makes it less plausible, like "if he was imagining it, why would he imagine A and B, instead of the more straight forward C and D?".

Or as DVK puts it, does the content of the books match up with what would have been imagined by a child escaping from the abuse? Does it suffer from internal inconsistencies endemic to such imaginings?

Answer

I don't think J.K. Rowling wrote the Potter series with the intention that it should be ultimately perceived as only a great fantasy by an unremarkable boy somewhere in Britain named Harry Potter. I mentioned in a comment above that I'm pretty sure JKR specifically addressed this in an interview once; I will continue to look for the quote and will edit it in if I find it, but it's my recollection it was made by JKR in an offhanded, kind of "Yeah, right!" manner while bantering with the interviewer. It is my recollection that she was definitely dismissive of the theory.

Here's a quote from JKR that I believe supports us, as readers, in taking the series and her premise -- that Harry Potter is indeed a boy wizard who finds the magical world to which he really belongs, and his story is real. MA is Melissa Anelli of the Leaky Cauldron website and ES is Emerson Spartz of Mugglenet.

MA: It goes back to the question of whether Snape is a double-double-double-triple-

JKR: [Laughs] Double-double-quadruple-to-the-power-of - yeah.

MA: - whether this had been planned, and since Dumbledore had this knowledge of Draco the whole year, had they had a discussion that said, "Should this happen, you have to act as if it is entirely your intention to just walk forward and kill me, because if you don't, Draco will die, the Unbreakable Vow, you'll die," and so on -

JKR: No, I see that, and yeah, I follow your line there. I can't - I mean, obviously, there are lines of speculation I don't want to shut down. Generally speaking, I shut down those lines of speculation that are plain unprofitable. Even with the shippers. God bless them, but they had a lot of fun with it. It's when people get really off the wall - it's when people devote hours of their time to proving that Snape is a vampire that I feel it's time to step in, because there's really nothing in the canon that supports that.

ES: It's when you look for those things -

JKR: Yeah, it's after the 15th rereading when you have spots in front of your eyes that you start seeing clues about Snape being the Lord of Darkness. So, there are things I shut down just because I think, well, don't waste your time, there's better stuff to be debating, and even if it's wrong, it will probably lead you somewhere interesting. That's my rough theory anyway.

_{Mugglenet Interviews J.K. Rowling - 07.16.05}

In another instance, JKR seems to confirm that Harry's world is real (in the series). Here, she's talking to a Leaky Cauldron staffer about an idea she had on how to present a written Harry Potter encyclopedia once the series was completed:

JKR: Well, to be honest John, at the moment, I'm not going to say "Don't hold me to this," but I'm just gonna say "This might change," but I imagined it as half of it, maybe on facing pages, but that might be difficult just through layout. But the ideal would be to have, say on the left-hand side, you've got a page showing all your back story, extra details on characters, or an entry on wands, showing what every character's wand was, and all of this stuff. And I think also it might be interesting to have information about the actual writing, and what I discarded. So on one side it's acting as though the whole world is true, and it's giving you extra information on that real world and on the other side we're admitting that it's actually fiction, and I'm showing discarded plots, characters that didn't make it, problems in the plot. I think both lots of information are interesting, so it would be nice to unite both of them.

_{Pottercast's Interview with J.K. Rowling - 12.23.07}

Neither of these quotes is the exact one I wanted to share, but I think they demonstrate JKR's intentions regarding the wizarding world and her vision of canon. In the Harry Potter series, Harry's world is real. It is not a fantasy on Harry's part.

IIn psychology, what you're asking about is called a paracosm, which is "a detailed imaginary world, or fantasy world, involving humans and/or animals, or perhaps even fantasy or alien creations. Commonly having its own geography, history, and language, it is an experience that is often developed during childhood and continues over a long period of time: months or even years." Paracosms are ascribed to early childhood trauma and are thought to be a way for a child to deal with early loss. Many works of fiction are cited as examples of paracosms, including the Narnia series by C.S. Lewis and The Lord of the Rings and The Hobbit by J.R.R. Tolkien. I think the Harry Potter series could be a candidate for paracosm by definition alone, but I also think JKR has been sufficiently clear that she did not write her books with that intent.

So, you asked if the content of the books match what would have been imagined by a child escaping from the abuse and the answer is yes, yes it does. Does it suffer from internal inconsistencies endemic to such imaginings? No, it does not.