I had never thought of using my Mac in this way, but thought it was a good use of a computer in an unusual way.
Yesterday I had gone to talk to a co-worker who was getting ready to head out the door for lunch. Rather than take out a compact, or find a mirror with which to check her hair, she just fired up PhotoBooth and used it as a mirror.
[robg adds: I've had this on sitting in the queue for a while, just waiting for a quiet hints day on which to run it...and that day is today. It will be interesting to see how many have done something similar -- personally, I never would have thought about doing this, mainly because I avoid mirrors whenever possible :).]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20091120091206439