Nice write-up on how to setup a raspberry pi to mine bitcoins. Sad part is its almost next to impossible to get any with such a small CPU. I did set this up myself about a year ago, with litecoins, and well..I guess if its already plugged in you might as well have it do something. Not so sure this something was a good thing…
http://www.linuxuser.co.uk/tutorials/mine-bitcoins-with-raspberry-pi