Its uses are limited—it exists solely to help train its user to throw a perfect serve height (A high, confident toss made 30-60cm. inside the baseline allows the server to uncoil both upward and forward into the court, making contact at 1.5 times body height)—and it might not be terribly practical, but you have to admire the ingenuity. Preemptive sic:

I poped (ed note: this is my favourite new verb) open my wiimote soldered in a few wires to the minus key and then taped the wiimote to left arm (I am right handed). Then I taped the other end of the wires to my thumb and wrapped a tennis ball in aluminium. So now when I had the ball in my hand it completed the circuit and pressed the button which registers the data in the software. I then toss the ball and when it leaves my hand it unpresses the button stopping the registry of the data from the accelerometer.

From here, our intrepid inventor is able to feed his data into a laptop to calculate his throw height and adjust accordingly. Clever. [Eyes on Tech—Thanks, Mans!]