WPI reports on a new experimental 3D mouse. The sensor is attached to a ring, and the ring worn on a finger. Wave around the finger:
...the mouse is designed to permit a computer user to control and manipulate items on a computer screen just by pointing at the monitor. The mouse uses an array of receivers to track the motion of a tiny ultrasonic transmitter worn on the index finger like a ring. Zooming is achieved by moving the hand nearer to or farther from the screen.
The problem may be similar to that of vertical touch screens -- I could see arms getting tired after a day of unsupported hand waving. Once again, gravity is the enemy.
Still, congrats to the students who designed it! Lots of details here, including a video.