I love the concept of earth hour - when everyone in the world hopefully takes the time to turn off their lights for one hour. Reduce the energy used, and take note of what you didn't need to be using in the first place.
On a grass roots level, it must be making a difference as my kids turned off everything an hour early, and ensured that we did our part. I love that their generation is going to help make green decisions to make the mistakes of the past, just that, the past.
And of course, the darkness and candles allows me to play with a few settings on my camera.