Just saw over at Mashable that Google hid a rudimentary flight simulator inside Google Earth. Pressing Ctrl+Alt+A (Windows) or Command+Option+A (Mac) opens a dialog window where you can select one of two aircraft, your starting location and whether or not you want to use a joystick (keyboard and mouse are also supported).
I had often thought it’d be nice to combine the open-source FlightGear Flight Simulator with the ground imagery of Google Earth/Maps. This is a step in the right direction but it’s hard to say if Google would ever go that far. It’d be nice, though.