Shelfari is Amazon’s answer to Goodreads. It has a pretty robust interface and you can deposit reviews and whatnot just like GR, but the traffic and communities aren’t quite as jumping as far as I can see. One thing I like about Shelfari is the book data page. If you are indie, this can really help your book shine with or without spoilers. Information like places, characters, plot points and themes can all be spelled out here in as much or as little detail as you care to release. This is also a great resource for the reader who really wants to dig deeper than the book jacket’s description, but doesn’t want to spoil it all by reading the free cheddar online.
If you are interested in some of the finer details of my book The Ancients and the Angels: Celestials, come take a peek into my book’s Shelfari Page. It’s probably the most comprehensive source of information an author can use to describe their products without giving away too much.