WTF would you use a balance board for in Linux?[..]this is just pointless.
No, you have no imagination. You can use the Wii Balance Board as a surprisingly accurate set of scales according to many sources. As they can be picked up for less than £20, it sounds like a cheap alternative to expensive Bluetooth scales. Connect a bluetooth receiver to a Pi and you could graph your weight loss, present it as a HTML5 app/website and access it from your phone or PC. For under £50.
Another great example would be measuring balance. This is again usually the domain of expensive fitness/medical equipment, but with the same hardware as before this would be just some code away from reality. Really cool.
Man, those two ideas were just off the top of my head. It must suck being you.