I read this today at Kottke:
Playing on a moving subway train adds an extra level of difficulty to accelerometer-based iPhone games. Not only do you have to contend with the in-game physics, you also need to compensate for the real-life accelerations, twists, and turns of the train. The effect pretty much tears your brain in half.
Which seems very intersting, and means that I have to get a decent game for the iPhone and ride the tram to work one day.