Here's an interesting new game coming out for the DS in Japan which does something with the microphone besides having players blow into it. Dragon Tamer: Sound Spirit is basically your standard Pokemon monster battling game, but in order to get new dragons, you record sounds from different instruments and sources with the DS mic.
This is kind of like what Monster Rancher for the Playstation, where different random CDs would generate monsters with different statistics and abilities. Bandai also did something similar with barcodes during the late early 90's with a reader that would do the same thing for the NES, SNES, and GB.
I'm intrigued at how the software is going to generate these dragons with the sound recognition software though. Some things that might be sampled and analyzed could be pitch, volume, tambre, tone, etc. It might be neat to see that a sound with a higher pitch would in turn give you a faster dragon, etc. It seems interesting though, I'm very intrigued and I hope this comes to the US. Let's just hope the gameplay delivers through the gimmick.