From a great story on Jan 5 in The New York Times by Martin Fackler, some of the ways Japanese homes conserve energy:
1. No central heating.
That's right, they only heat a room when it is being used.
2. Fuel cell.
Not available in the U.S. yet, but home fuel cells convert gas into hydrogen, which the fuel cell then uses to generate electricity.
3. Energy efficient appliances.
A frig that beeps when it is left open, a compact dishwasher.
4. Reuse water.
More than one person uses the same water for baths, then they wash clothes with the still warm water.
5. Tax breaks.
The government provides tax breaks for buying energy efficient appliances.
6. Smaller residences.
The average home is about 1,100 square feet, compared to 2,800 sq. feet for U.S. homes.