Well, Earth Hour is coming up tomorrow, (28 March, 8:30PM). It's an hour when people voluntarily turn out the lights to mark awareness of the link between energy generation/use and climate change. Last year, Google joined in the fun by making their front page black (I don't remember if it was just for an hour or a whole day). The event is organized through an official web site at earthhour.org.
An article on Yahoo! news cover the "event." Toward the end, they quote Bjorn Lomborg (infamously of the skeptical environmentalist), saying Even if a billion people turn off their lights this Saturday the entire event will be equivalent to switching off China's emissions for six short seconds." This followed a sentence saying, "Critics said the initiative was little more than empty symbolism."
The whole point is to make a gesture. It's like wearing an AIDS ribbon (back in the days before it lost all meaning). The ribbon doesn't cure AIDS, and turning out your lights doesn't change global warming. But if the Las Vegas strip is dark for an hour (as planned) and the Sydney Harbour is dark for an hour, and now even China is joining in, that is a meaningful gesture. It shows how far we are coming (despite my previous post) in educating the public about the dangers of climate change.
Plus it reduces light pollution, which is a good cause unto itself.