Top-ranked books at Amazon.com: the rich-get-richer effect

There's a new collaboratively written book, Worldchanging: A User's Guide for the 21st Century. In an attempt to gain visibility, and therefore sales, the creators of the book are openly "hacking" Amazon. By concentrating sales in a 24 hour period, they're trying to boost their Amazon sales rank. It might be working. They're currently ranked #14 (I don't know where they were ranked before).