The iPhone has an accelerometer to detect if you tilt it (to turn the browser or picture) or when bring it to your ear (to dim the screen), which is quite clever. A few months ago some videos popped up with people showing how they controlled content on their pc with a Wii remote. So it was just a mater of time till similar projects for the iPhone appeared. Of course this is way more interesting as you have a screen in ‘your game controller’. You can read more about it here.