Well, after a week of investigation, I’ve settled on a social network for books: Shelfari. It’s attractive, easy-to-use, easy to manipulate many books at once, they have a mobile version, and I have one friend on it (who invited me).
Goodreads.com also looked nice, and it almost won. bookwormr.com, the one I originally found was just too immature at this point. I’m also wondering what features are going to set it apart from the pack, especially when there are so many well-established sites that do the same thing.
Meanwhile, if you want to read some books that will definitely NOT make you smarter, check out 5 Books that can actually make you stupider.