Harry Potter and the Deathly Hallows has apparently been leaked via Bittorrent.
Note: I haven’t downloaded a copy via Bittorrent (or even used the above link).
Although a violation of copyright laws, my guess is that it will have little or no effect on book sales. Die hard fans are likely to preemptively download a bootleg copy and still read the print edition when it arrives.
The big issue is whether you or I will be able to avoid spoilers on the Internet until we can get the actual book to read.