I had good time hacking with this, and in the end was able to make a game where you keep a ball inside the square with an accelerometer while another person can adjust the game speed with the IR sensor. When you lose, you get appropriate sound and screen animation (doesn't look like much, but this is usually what takes the most coding time).
coworkers at work :)
my first try
someone made an almost working pong game
another keep the ball in the square game
My finished device in smal form factor fitting on top of the arduino
Here's my demo to my coworkers, using my external clean power supply:
And the same thing in a small form factor, using the noisy arduino voltage ref (this is why it's moving so much in the init phase, despite no input). I'll have to do some analog electronics to clean that up:
This was definitely time well spent and a good learning experience.