This was apparently just released:
http://www.gta4.net/map/
Obviously it's more relevant to street-based games, and probably uses orders of magnitude more server space than just rendering the game from the original data, but it's still clever stuff :)
Wow, that's awesome. Must take tons of space.
I wasn't too impressed... until I realized it had full street views. That's amazing. :D
I got a whole bunch of virus warnings when I clicked on that--just sayin'.