No idea for how long this has been around, but I only today discovered the
flight simulator in Google Earth. Yes, there is a (quite basic) flight simulator built right into Google Earth, starting with version 4.2. There is no sound at the moment and only a few basic moves, but you can at least use your mouse (I prefer it over the keyboard) or even a joystick. You'll want a fast internet connection, too, and probably some basic experience flying a flight sim. Well, my experience stems from F/A Hornet back in 1998, but it's enough to keep me in the air.
You can
find a list of commands here, and also the instructions on how to start the simulator. Two planes are available today, start the sim with Command + Option + A on a Mac (or Control + Alt + A on Linux/Windows), and there you go. When the simulation starts, click the viewport with the mouse to get mouse-control, it's easier to fly like that IMO.
Beautiful!

Rafael: Thank you very much, I was having a huge headache to solve the very same problem!