I discovered a little app called lilt the other day
http://www.jonn8.com/lilt/
It allows you to use the inbuilt sensors in the hard disc and the sensors for the backlit keyboard for all kinds of things.
Basically imagine using your hand to wave over the light sensors to load and app or doing anything as you could tie it to an applescript that maybe runs a backup!
Its great I had a few issues with it, but having spoken to the author I'm certain is down to the hardware sensors.
I use it to load mail or switch to mail as well as address book by holding my hand over my mbp's speakers