Well, evidently GM has brought out a hybrid car that will work pretty much like a diesel-electric locomotive. A gasoline engine drives a generator, batteries drive a motor. The Volt is a fairly typical compact car otherwise, and should retail for somewhere between $30,000 and $40,000. Let's see what happens if it indeed eliminates the cost of gasoline for a driver who commutes 10,000 miles or so per year--250 days of work times a 40 mile round trip commute, and let's compare it with the Cobalt, built on the same platform.
Pricing for the Cobalt starts at about $15,000, and its real world mileage is probably about 30mpg. The 300 gallons you'd put in it each year would set you back about $1200. The electricity to charge it? Battery capacity is 16kW-H, so you're going to spend about $400/year in juice to charge it.
The flip side? Well, you've just paid double or more for your car, and hence the annual cost of owning a hybrid is about $2000 to $3000 over that for the Cobalt--10% depreciation and 5% interest on $15000-$20,000 excess cost. One could theoretically break even if the price of gasoline got to $10-15/gallon, but remember that the price of electricity will increase as well because all that coal is brought to market by diesel powered locomotives.
So if you've got an extra $10-15k in your bank account that you want to use to help the environment, may I suggest a new bike?