The guys behind Guild Wars II took some taxis, decked their interiors out in fantasy livery, dressed the drivers up as game characters then set them loose to pick up actual passengers.
Things seem to go surprisingly well! Though most footage was captured during the daylight hours. I'm sure trying to clean puke and kebab remains out of those fancy seat covers at 3am wouldn't have been as fun.
Especially since Seth Killian was in there.
Guild Wars 2 — The Great MMO Migration [YouTube]