An interesting evolution of gaming with the use of terrain and metadata from Google Earth.
Google Earth And 3D Warehouse Opened Up To ‘Game Developers

Second life brought you the experiences of a virtual world. In this case virtual worlds are created using real data.
See John Battelle´s post, Google v. Second Life? No Contest:
I’m going to guess that Google’s version is going to be all about reality, and mashing up AdWords, Google Earth, Sketchup, and the Yellow Pages/Google Local. The two will live quite nicely one next to the other, and most folks who use one will probably not see using the other as even