Fancy chatting online about books and don't think existing social networking sites like Facebook quite cut it? The Reading Room is a social network specifically for book lovers.
Locally developed (and launched in beta this week to coincide with the Sydney Writers' Festival), The Reading Room includes features to let you add details of your own library and rate titles you've read. You can track particular authors (so you receive notification when they release a new title), participate in forums, join reading groups and (inevitably) purchase books you're interested in via Amazon.
The feature set is pretty similar to BookArmy. The add books search is a little fiddly and there's a few beta glitches to iron out, but for serious readers this is a potentially handy tool. The Reading Room is free to use, requires signup.