I was working on a book social site where users earn badges after reading books. (Basically Foursquare for books. There would be badges for reading the top 10 books of a genre/author, milestones, etc.)
Thanks. I was relying on book lovers' desire to "show-off" about how well read they (we) are.
I started using Amazon, but when I started thinking about adding badges and it would need the book database to be very specific about authors/genres/titles, (which Amazon's wasn't) I realized it was way out of my league.
Gave up on getting a good book database.