I thought I heard this earlier some time ago.. not sure, if this new!!

"Not Satisfied with just Planet Earth, Google has gone ahead and started mapping virtual worlds. In this example, Google maps is used to power A Map of the Burning Crusades expansion of the most popular MMORPG ever, Worlds of Warcraft."

http://seoblackhat.com/2007/04/28/google-maps-worlds-of-warcraft/

No Peter.. it's not new... :/
http://blogoscoped.com/archive/2007-04-06.html#n12

And you've always had the option to use custom maps with the Google Maps API...