Somehow this missed my radar, but last Saturday at 8:30 pm, 26 March 2011, people around the world observed Earth Hour. This event started in 2007 in Sydney Australia.
The intent is not for one hour of darkness to have a major impact on energy efficiency, but for people to participate in an global activity and think of ways they can make improvements. I like the idea of group participation and global responsibility.
For great photo comparisons of cities that observed Earth Hour, see this Boston.com article.