In the Washington Post dated 6/2/07, there is a fascinating article by Alan Sipress about law enforcement in virtual reality worlds. Personally I think VR worlds are going to be huge once the graphics and user interfaces improve (along with system performance, of course). Already, VR participants have experienced a range of two-way bleeds between the real world and VR. Sipress's article documents that real world law enforcement has been pulled into VR. Highly recommended.
The image above is a piece of a map of Second Life, a popular VR world. I made a screen shot of an edge of that world. I wonder if the Flat Earth Society has opened a chapter in Second Life.