In recent months the number of Toyota Prius hybrid cars in my Albany/Berkeley neighborhood in the San Francisco East Bay has skyrocketed. They're everywhere, suddenly.
This part of America is known to be more liberal, anti-war and environmetally-conscious, so people have been more willing to buy these cars that run on a mixture of gasoline and electric power: every time you press the brakes, it generates and stores electricity.
Northern California also pays more for gasoline than the rest of the country (close to $3 per gallon). So it makes perfect sense: hybrids can get around 50 miles per gallon.
The rest of America is catching up as well: you have to wait up to a year to get your hand on a Prius. Honda and other car companies have their hybrids as well, but so far they have not been as successful as Toyota.