I know we were supposed to create a Library Thing account, but since I've been doing Shelfari, an equivalent to Library Thing, for about two years or so now I asked if it was ok to substitute. I have enough accounts, etc. without having to worry about updating one more thing.
I absolutely love Shelfari. I actually put my Shelfari widget on my blog. It allows me to add books that I've read, let people know what I'm currently reading, review and rate the books I've read and keep books in a "want to read" list so I don't have to have a bunch of pieces of scrap paper lying around with a million lists of books.
Since Shelfari is just for reading and there's not really any personal information posted with the exception of the "About Me" blurb, I'm much more liberal with accepting people as friends. If you read and we have similar tastes, I'll let you be my friend. Heck, even if we don't have similar tastes I'll let you be my friend. :)
I highly recommend Shelfari to everyone!