http://www.myearthhour.org/
For me, I intend to turn on every light on all three buildings on my property at 8 PM, and have every operable internal-combustion vehicle I own idling with lights on in the parking area, until 9 PM. I will also be operating all audio gear on the property at full volume for the duration.
I'll be riding the motorcycle. Not good to let it idle - it overheats. Beside, riding uses more irreplacable fossil fuel, and emits more of that horrible pollutant, CO2.