As an F1 fan, this is something I've been wondering about recently....

I keep getting the urge to build a fully electric car but, when I do the sums, the results either end up being pretty pathetic or the cost of batteries is just flat-out ridiculous.
Occurs to me, however, that it shouldn't be that hard to add an electric motor to an IC engine to create a hybrid or create a KERS style system.

At it's simplest you'd need to hook a leccy motor in line with the IC engine, use it to charge batteries in "recovery mode" and then, at the push of a button, you'd have an extra 50-odd bhp for a couple of minutes.
I did some cigarette-packet calculations and it seems like a single "bank" of 4 heavy-duty 12v batteries (72v @ around 100 Ah) would achieve this.
On a more complex level, if you could find a way to feed the electric power into the transmission, rather than the engine, you could create a true hybrid, where the car could be put in neutral, the IC engine stopped and drive applied solely from the leccy motor.

Must admit, I don't really have any real plans to implement such a system myself but, with cars like the McLaren P1, the Porsche 918 and the LaFerrari starting to appear, it seems like hybrids are starting to make the news and I was just wondering if anybody else here has considered this sort of thing or whether anybody's actually built anything similar?