Well, being the giant harry potter nerd that I am, I've ended up with both of the fake ones, and read more of them than I should have. This new one coincides with that "leaked first chapter" on
www.mugglenet.com, and the shear intensity of what a hoax would have required for it to be this realistic gives me reason to believe it's definitely legit.
Edit- Also, it's not a .txt, a .doc, or a .pdf. It's 256 photos of the book. You can see the binding (which is yellow on the spine and green on the edges) as well as chapter art for each chapter (which all look new and are perfectly in the same style as the chick who does all the US artwork). This would have been such an undertaking to fake.
The first chapter is also ****ing awesome, which alone is the best evidence that it's real.