I'm currently trying out different sites to figure out which one I like best. I was using weread through Facebook, but decided I didn't like the setup for my library. I'm using goodreads and shelfari, but thank you jgaiser for Library Thing! I'm going to have to check that out too.
goodreads is nice, and I like it best for the library organization. However, I think it's a bit lacking on the social networking side, and am trying to find a solution that keeps the strong organization but allows for more networking.. I also don't like goodreads' (and shelfari, for that matter) interface into FB.
The exploration continues...