On Feb 12th i mentioned Ning in my post. I certainly was intrigued the first time i went to their site but it was only this evening that i got a chance to check it out in detail.
With its cloning features, within 30minutes i had set up a Bookshelf Ning where i can create and share book lists and reviews. The Best thing is that all the book information comes from Amazon so i had to setup a Web Services account with them which was super easy, so it shows off a little web services API action as well.
Ning allows you to create Social Web Applications in a flash-there are tons to clone from- awesome stuff
You can find my bookshelf here: http://readingiscool.ning.com and I will also add it to my links.
I also love the way they are displaying the tags that the users are applying.