Did you even read the article? It says:
But the motion sensor does more than just notice sudden movement: It can be used to determine the angle the PowerBook is tilted at in any direction, along with the velocity at which the computer is being moved.
Enterprising hackers have discovered that because the new motion sensor returns reasonably accurate measurements to Mac OS X, it can be used to do some cool tricks, from realigning an image in a window so it always points up, no matter what angle you hold the laptop at, to controlling what's playing in iTunes -- rock the machine backward to go to the next track, forward to play the previous one.