This past week I have a had a number of traditionalists ask me about second life and virtual worlds.
Second Life is a 3-D virtual world entirely built and owned by its Residents.  Real User Generated Content.  A virtual world is a computer-based simulated environment intended for its users to inhabit and interact via avatars.  However there are a number of successful virtual worlds.  Furthermore, there are a number of great resources on this topic.  Here are a few of my favorites.

http://s3.amazonaws.com/slideshare/ssplayer.swf?id=110710&doc=virtual-worlds-and-vet2647

Virtual World Resource List

ON: SecondLife & Virtual World 101 via @jpenabickley