Pops, I agree with your thoughts about car-pooling, telecommuting, etc. There's a whole slew of ideas like this that could/should be incentivized (?) by tax code.
Re efficiency, Wikipedia (http://en.wikipedia.org/wiki/Electric_car) states (as an example only) that the Tesla's plug-to-wheel energy use is 280 W·h/mile. A gallon of gasoline contains approximately 32kwh of energy, therefore the Tesla can go about 114 miles on an equivalent amount of energy found in one gallon of gasoline. The Lotus Elise is what the Tesla is based on. 2005 and earlier Elises have EPA gas mileage ratings of 23/27 mpg (city/hwy). I understand the later models get a little better (approaching 30.) Regardless, it's easy to see that the electric version is many times more efficient even though it's heavier. Well-to-wheel efficiencies aren't included in the gas mileage of the regular Elise but that's a small loss.
My own conversion (1994 Toyota Pickup lead-sled) uses about 333 kwh/mile (measured with a meter at the charger, supplied by solar panels on our roof BTW) so would go about 96 miles on an equivalent amount of energy found in one gallon of petrol. Stock mileage is low twenties so the ratio is about the same. The efficiency of new vehicles is getting better and better but ICE's will always be constrained by Carnot.
CalCars is pushing big time for mass conversions of existing vehicles to plug-in hybrids. I believe there are some startups out there looking at this but it'll still take a long time to switch a majority of our vehicles.
Carbon Tax Baby!