There are a lot of reasons to love goodreads.com--you can keep track of what you've read and what you loved about it, you can compare book tastes with friends. But for published authors, here's another reason: they facilitate book giveaways for you.
I've done this twice and been amazed at how many people entered the contest. I think it was something close to 2,000--2,000 avid readers. (Granted, my last book was for adults, but still. Children's literature is very hot these days.)
It's really easy to sign up, and you just need to be willing to send a copy of your book to the winner. (You might want to restrict to U.S. recipients if international mailing isn't your thing.)
The rest of the details are here.