1) Not all energy comes from burning fossil fuels. Nuclear, Wind, Solar and Hydro could also be used to power an electric car. That alone should make it comparatively cleaner.
2) As for efficiency goes, in a car about only 15% of the fuel energy is converted into motion. The rest is wasted as heat. Power plants are more efficient at using that heat and turn it into electricity, making again electric cars get more efficiency per unit of fuel burned.
3) Gasoline must be carried to gas stations. Think of it as a hidden energy cost: The cost of running you car = the fuel it burns + the energy it took to get it to your car.
On the opposite side, batteries are not as efficient storing energy as gasoline is, and there is also loss of power on transmission lines. I haven't done the math myself, but overall electric should be more efficient than gasoline cars.
