I spotted this recently whilst reading through my favourite feeds. Take a look at the video as it is quite difficult to explain how it works only using words.
In summary: “RjDj is a music application for the iPhone. It uses sensory input to generate and control the music you are listening to.” [excerpt from the RjDj website]
I just think it’s a concept that has scaleability.
If you download it I’d be interested to hear your comments.