They built an accelerometer based Bluetooth mouse. They ended up creating a mouse that maps rotational movements to x/y motion.

This cool mouse is handmade in Japan from ‘Chinese flowering Ash’ and it has a built-in accelerometer like the iPhone that lets you control the cursor on the screen.

Okay, all you Arduino fans, now that you've mastered the basics of blinking LEDs, driving motors, and monitoring environmental sensors, you're ready for something a little more interesting, right ...