Energy Star has released information about the Energy Star Water Heater criteria that will take effect in January 2009. This is exciting news, as water heaters had not been Energy Star certified prior to this, and it will help people make informed decisions about products' energy efficiency and potential long-term cost savings.
Link: Eric Helton: Building Science -- Energy Star Certified Water Heating (HGTVPro.com)
Since we bought a water heater recently, I checked it out to see if it had the Energy Star, but it doesn't. However, it's self-cleaning (I wonder how that works.), and it has an energy guide showing its ranking with other water heaters, and it says that it should cost about $415.00 to run each year. ('Course our electric bill continues to rise.)
In a recent Paul Bianchina e-newsletter, he points out that if you add a bathroom, you may need more hot water.