Library Thing is cool. I won't use it very often, so I didn't sign up, but it's good to know it's there. I love books, of course, but these days, it's all about going to the library and letting my child pick out some great childrens books.
I'm always looking for books that I can use in the music room. Books that can be broken down into rhythm or that have some music to them are great for my kids. So, I will probably use the site to find other musicians who use books in the same way.