Feature: uses internal accelerometer(s), shock sensor, or similar functions at the hardware level as input for output that describes the motion of the phone/laptop in terms of Richter scale (yes, the earthquake Richter scale).
Reference: BLDGBLOG: Earthquakes in the Sky is the post that got me thinking about this. Many thanks to BLDGBLOG, which should be recognized in some way, perhaps with a persistent link in the credits.
Reward: $50 for first working version. Submissions to email@example.com. I will be able to test the laptop version myself and will have to distribute the iPhone version to a colleague. All submissions will be recognized here.