At the summertour with the illutron ship ( www.illutron.dk ), we had dancers crawling all over the cargo room of the ship.
In the ceiling, I put up a load cell connected to an Arduino board via a millivolt amplifier.
Using the weight of their bodies, the dancers could change the music and control the light.
I have compiled some video and technical talk here:
http://cerulean.dk/words/?page_id=42
This is my first attempt at making some sort of documentation for an Arduino project, so please bear with me 
- But do let me know what you think! Any other ideas or things that spring in you mind.
(Sorry for the inconvenience of comment-approval at my site, but I have been a spam-victim. )
Best regards
Christian Liljedahl