Did you know? - Sudden Motion Sensors

"In January 2005, Apple introduced the Sudden Motion Sensor™ (SMS) in its high-end laptops. The SMS is a three-axis accelerometer linked with the hard disk, so that if the laptop suddenly finds itself in free fall it can anticipate an impact and park the hard disk heads in a safe area, thus reducing the effect of the impact. Apple included the SMS in all its laptops starting in July 2005. IBM had begun including a similar feature, the Active Protection System™, in its ThinkPad laptops two years earlier; Acer Inc. is just now releasing its GraviSense™ utility."

-Source: http://www.seismosoc.org/publications/SRL/SRL_77/srl_77-6_es.html

Cool isn't it. Whats better is the fact is that the accelerometer reading, usually of (x,y,z) axes can be read and used by programmers, though Apple didn't intend it to happen!

One such application is Seismograph reading (the above link.)

Some other cool programs found in youtube:
http://www.youtube.com/watch?v=I6ZpsqOD4rU&eurl=
http://www.youtube.com/watch?v=aBJQ5085kSo

With such an interesting tool, the possibilities are just infinite.
A brief description on how it works can be found here.

the end.