I learned that Earth Hour is tonight at 8:30pm for those in Eastern Standard Time (8:30 pm in whatever your local timezone is). For an hour people participating will simply turn off their lights for one hour "symbolically calling for action on climate change." It's held every year during the last Saturday of March.
It was created by the WWF. Last year they estimate 80 million Americans participated. Here in New York, landmarks like the Brooklyn Bridge and Empire State building also took part. While I'm a fairly cynical person, this is an easy gesture I'm willing to make.
Even Vegas Is Going Dark: http://www.ktvn.com/Global/story.asp?S=12214212