From all the Metaverse-style worlds out there, SecondLife is my favorite. I tested it once, and now I just try to stay away, it's addictive.
Today, I came across a SecondLife Amazon integration that's just too cool not to talk about. There is a store inside SecondLife, called Life2Life, that uses the Amazon Webservices to show your books, magazines and even perform searches.
Every day goes by, and Snowcrash feels more real.