Most of the games and other apps I have seen that use the iPhone and iPod Touch's motion sensing capabilities are difficult to control (like aiming at things in a game) or really gimmicky (shake to get a result instead of pushing a button!). But this new turntable app for the second generation iPod Touch (no other version and not the iPhone) is very clever and cool, if not necessarily useful.
As Gizmodo explains, "It works like a turntable, changing the speed depending on the revolutions-per-minute." It's not in the app store yet, but I don't see how this doesn't become popular if/when it does. And if it gets improved and starts including the ability to scratch and control tracks precisely, it could actually become useful to DJs and a respected little part of the music industry: