My son just sent me an email about Second Life. It is absolutely amazing and I am just beginning to grasp all its dimensions. It is basically an unlimited virtual world constructed by its residents. It actually has its own currency and an exchange rate with the dollar. The money that people are making in Second Life is most definitely NOT virtual. A Lady in Germany is making $175,000 per year designing virtual homes.
HERE is a fascinating video of a presentation by its creators.
LOTS of YouTube videos about Second Life.