Earth Hour is the invention of the World Wildlife Federation, and of course everyone green is jumping on board. (Arlington County's government is promoting it.)
The idea is that at 8:30 pm (your local time) everyone turns out their lights for an hour and "votes for earth."
Sorry, but this is silly. We have no plan to sit around in the dark for an hour on a Saturday night, twiddling our thumbs to "vote" for earth. There are far more meaningful ways people can "vote" for earth, without resorting to some gimmick of dubious value.
We would contrast "earth hour" with Earth Day, which is a good event. Earth Day becomes a focus for a number of green activities, without everyone sitting around in the dark for an hour.
Sorry to be so Curmudgeonly, but at our home tomorrow night, our (fluorescent) lights will be on (to the extent we need them).