A new social network is emerging as an exciting contender globally and growing really fast. Pinterest works as a series of 'pin boards' which allows fans to share interesting images/video/media with friends in a very quick and compelling way.
The viral element (like 'liking' on Facebook and 'reblogging' for blogs) is quite interesting as pinning something to your board only takes a couple of clicks, and the boards are very visual - ideal for the current generation who really like imagery and image heavy blogs.
All authors should join this - not just becuase it will help sell books, but it is also a nice resource to generate and drive ideas.