During a recent visit with Apple, someone tried to convince me to test out the motion detector in my iBook by tossing it up in the air and catching it on the way down. I took his word for it. Never occurred to me that there was a spiffy widget to be made out of that feature. You can use it to play Marble Madness, or as a straight-up leveling device. Granted, it would be far more useful if the level worked via some kind of USB extension so that I didn't have to hold my laptop up to the wall just to hang a picture. There is a good collection of videos of these apps in action over at Make today.
Use a PoweBook as a Level [Make]