Game on Google Maps offers a very good overview of the existing games that take advantage of google map. It ranges from very simple concept (finding a landmark) to more elaborate. With also ideas for possible implementations (Warcraft-like games or Risk or a revival of Where in the world is Carmen Sandiego?).
An interesting existing project is Brewster Jennings Protects America: The global spy hunt game.:
Remember playing "Where in the World is Carmen Sandiego" as a kid? Well now the new game Brewster Jennings Protects America brings this classic adventure into the 21st century by merging the game play with Google maps technology*. In the web-based Brewster Jennings Protects America game you race around the globe as a government agent trying to stop a deadly terror attack from taking place....
The story so far: You are an undercover CIA agent claiming to work for the fictitious "Brewster Jennings & Associates" company. You were just awoken at three in the morning by a phone call from The Chief telling you to report to your office immediately. From what he told you it looks like a terrorist is set to attack today and you are the country's last and only hope.
The "control your airplane" is almost an old-school shoot'em up with a google map.
My favorite is maybe Tripods in which you have to battle invading Google Maps tripod markers that are invading Manhattan!
Why do I blog this? with open platforms such as google map, there might be an opportunity to have creative location-based games/applications (with of course still some user interface issues).