Nice list of simple ways to save energy and lower the bills -- courtesy of the State of Maryland
http://energy.maryland.gov/Facts/est.html
Personally, I think the water heater can be set lower than 120 degrees --- that's still pretty hot. If you're worried it's not hot enough for the dishwasher, use the "high temperature wash" setting. That way, you're only using very hot water (and extra energy) for washing dishes.
