Well, one thing that comes to mind is sites like LibraryThing where you upload your "library" (or rather, titles of the books you've read), and it will come back to you with automatic recommendations (you like X, other people who like X also like Y, so you might like Y) and put you into contact with other people and so on and so forth.
http://www.librarything.com
I don't know if this works without logging in, but this is my LT page, you might get a better idea of what I mean:
http://www.librarything.com/home/acidzebra