Not content with resting on their sensory laurels, Nintendo decided to just go ahead and make another bizarre form of input (since it seems to be working so well). The upcoming DS title Slide Adventure: Mag Kid (which could use a better marketing team) will feature a "slide sensor" that fits in the GBA slot of the DS. It extends outwards onto the back on the DS, and when the device is placed on a flat surface, the sensor can pick up the sliding motion of the entire unit on said surface.
It's a little weird, but it's got some cool potential. It does, however, reduce the true portability of the device, rendering both bus-play and toilet-play completely useless. And we sure do love our toile ... you know what, never mind.