Johnny Chung Lee's Wiimote-based user interface projects include a way to control your computer by waving your hands using an LED array and some reflective tape, and an electronic whiteboard anywhere using a projector, a Wiimote, and cheap homemade infrared flashlight pens. Johnny has released his software, and both projects look fun and easy to assemble. See his excellent videos.

Somehow it never occurred to me to think very hard about how the Wiimote operates. The Wii's "sensor bar" is misleadingly named: It doesn't sense IR signals beamed to it from the Wiimote like a traditional TV remote control. Rather, the IR sensor is in the Wiimote, and the "sensor bar" is just a couple of infrared lights. The Wiimote collects data from the IR sensor along with its accelerometers that detect motion and the game buttons, and transmits the data to the Wii via a Bluetooth connection. Johnny's projects use the Wiimote's IR sensor and a laptop's own Bluetooth capabilities to detect points in a projected 2D space.

A short article and slideshow on the Wiimote's IR and acceleration sensors from the NYTimes, 2006.