Google.com writes
"Google users in the United States will notice today that we "turned the lights out" on the Google.com homepage as a gesture to raise awareness of a worldwide energy conservation effort called Earth Hour.On Saturday, March 29, 2008, Earth Hour invites people around the world to turn off their lights for one hour – from 8:00pm to 9:00pm in their local time zone. Given our company's commitment to environmental awareness and energy efficiency, we strongly support the Earth Hour campaign, and have darkened our homepage today to help spread awareness of what we hope will be a highly successful global event."