read this. I know its a blog, but it shows accurate graphs of power usage in California.
http://wattsupwiththat.com/2009/03/29/earth-hour-in-california-success-or-bust-the-caiso-power-graph-tells-the-story/
notice, no decrease in usage or demand. If there is no decrease in one of the most liberal states, then the results around the rest of the country will likely not be much different.
those who are lazy
Saturday's graph:
Sunday's graph: