PS (More numbers)
Attention hugely annoying rant follows
From my previous "numbers" post you could assume that a 'leccy car can (in the best theoretical case) be 50% more efficient than a gas-powered one (20% vs 30% conversion efficiency). However, the Prius does have huge batteries+a gas tank+2 engines instead of one, which makes it 50% heavier than an equivalent gas-powered car. Guess what it does to you power consumption in the traffic...
Also, just to give some perspective, an ICE diesel engine does have a conversion efficiency higher than 50%. When you take the weight factor into account, it's twice the efficiency of the Prius. Whithout that nasty huge battery.
Also, even with a gas-powered car you can significantly decrease pollution by just switching the air conditionner off (I would hazard a 10% estimation, though I must admit that I just pulled this figure out of my hat). Oh, and if you want to reduce your, erm "carbon footprint", why don't you buy a smaller car? Fiat makes this nice lil' Seiciento -wich is incidentally an awful lot of fun to drive. Or a nice small turbodiesel 5-seater with no AC to avoid the temptation. Of course you'd have to find gasoil, but it's still much more convenient than overnight charging over the mains (even in the US).
Of course, all that is assuming that car-produced CO2 is a problem to begin with, which I do not really believe to begin with (even assuming that man-made CO2 is a problem, in the US 'leccy production accounts for 40% of total man-made CO2, and various industrial processes make for the bulk of the rest). But then, better safe than sorry, limitting energy waste and pollution is bound to be a good thing in the end. Only the Prius (or any hybrid car) is really not the solution.
Now I should mention that you can feed any modern diesel engine (with its 50%+ conversion efficiency) on 1/3 colza oil (crude, just filtered. The supermarket grade will do). Some car-grade diesel engines, and all industrial-grade diesel engines (tractors, lorries, harvesters, you name it. The injection pump is the key) can run on 50% colza oil. You will lose in the acceleration department, but win a lot in the torque department (in plain English, it means "you wont race a mustang on the next traffic light, but you won't stall ever again, even with the handbrake on"). Bonus: your exhaust fumes will smell like french fries. Really. (OK, maybe that's a malus finally). And with minor modifications, you can run those on 100% colza oil (minor modifications being mostly a pre-heating system: viscosity and flashpoint are the enemies here). Of course it's illegal to drive such a modified car on a public road in most countries, and thanks to the oil lobby it will remains that way for the foreseable future.
But in any case, the Prius with its max theoretical conversion efficiency of 30%, its huge toxic super-heavy battery (and most obnoxiously, its dumb smug driver) is *not* *going* *to* *save* *mother* *earth*. Get that?