I've been a member for a few years (transferred my LibraryThing account) and have loved it since.
It has the features to be a literary Facebook, but I don't really use many of those functions. I just really like adding, culling, and organizing my book lists.
It seems more socially acceptable than my past practice of regularly carrying and obsessing over book lists on my person. I know this is not normal, and one day I will seek psychiatric help.