Google Earth has already been used for a few games, like cheap flight simulators. Know what it hasn't been used for? A giant map to let you drive the A-Team's black van across.
There's no score to beat, no time to race, no objectives you have to accomplish, all you have to do is... drive around. Oh, and maybe unlock a few clips from the upcoming A-Team movie. But if you're not one to succumb to cheap online marketing pushes, then yeah, just drive around.
As a game, it's threadbare. As an example to other developers on what's possible if they try a little harder or spend a little more money, though, it's proving surprisingly useful.