Last year, Sydney, Australia, turned off its lights for an hour in order to save some energy. Mostly, it was a statement -- to see the combined effect of a lot of people agreeing that something needs to be done. The event was such a success that the World Wildlife Fund decided to take it global in 2008.

So on March 29th, whenever 8pm rolls around, over 350 cities in 35 countries, millions of individuals, the Sears Tower, the Golden Gate Bridge, and 2,100 corporations including HP, Coca Cola, and McDonald's, are all turning off their lights.