Some sites also have a piece of video on them showing the fan accessing the secret bit of JK's website.
It looks very much like the other parts of the site, so if it isn't real it's a very good-looking fake.
The rest of the text does seem in the style of JK's writing, and she comments that she's struggling to keep the book shorter than the Order of the Phoenix.
We're trying to find out if the title is real or fake, so keep checking the site for updates.