Reading social site

I was wondeering if there are any good social networking sites centered around "What I'm Reading." I know that many blogs and site authors tend to post what they are reading. And of course Amazon has numerous outlets to let the world know what you're eyes are checking out. Is there a decent site that is strictly devoted to what people are reading and incorporating other items like rating the book and even discussing topics. Could this be an interesting topic to continue to build upon?