@@small(still waiting for the almost-no-voltage-loss diode...and the battacitor...to be invented)

There are probably only about 4 people here who understand that syntax

Seriously, though the battacitor would be useful. There are already people talking about using a string of LiIon batteries (which have the problem that you can't pull high current from them, at least in the sizes I'm thinking of) and a string of ultracapacitors in parallel, such that you can pull high loads and drain the ultracapacitors when you need to, and otherwise just drain the batteries at a more usual rate (and recharge the ultracapacitors).

The idea of a car powered by ultracapacitors is amusing, but it would be more like a box-truck-sized trailer if you wanted any range.