well, i've read the first 10 chapters of that leaked/fake book in lrf-form. Although I did found some discrepancies, it's written quite well. Not really a punishment to read it, unlike the other fanfiction thingie that was out.
I'm not too sure if it's the real thing though, but I must say I'm fascinated by the dark force of internet >
The story has a plothole that I can't explain. And also, the sudden use of a phrase like "spread like cancer" does not seems JKRy to me... nonetheless, wether it's fake or not, it's a good read while waiting for the real deal, because it's written quite well if it's fake.