Going with the "Discussions about anything book/author-related" clause, I give you:

http://www.librarything.com/unsuggester

Unsuggester takes "people who like this also like that" and turns it on its head. It analyzes the seven million books LibraryThing members have recorded as owned or read, and comes back with books least likely [emphasis mine] to share a library with the book you suggest. The unsuggestions come from LibraryThing data, not from Amazon. LibraryThing also produces great suggestions.

I haven't played extensively with this yet, but it's been fun so far.