I've been a member of LibraryThing.com for a while, but was finding that the recommendations weren't enough to keep me there. On BookCrossing they were talking about GoodReads and saying how (well) good it was, So I had a quick look and thought it was worth joining.
I particularly like the social network side of it and the trivia linked to what you've read.
If you're on GoodRead feel free to add me as a friend. My username is AbigailAnn.