My 9 year old Nissan Pulsar gets 6.7 litres / 100km in actual driving and doesn't change much between urban and highway. If I travel to work during the peak it's about 25 km/h on average and the car gets much the same fuel consumption as cruising at 110 km/h.
Now, if I simply swapped the petrol engine in the Pulsar for a diesel then that in itself should drop the fuel consumption to about 4.7 litres per 100 km/h with nothing else changed. All things considered, that stacks up better in terms of resource use than a petrol-electric hybrid.
A diesel-electric hybrid would make more sense. Doing it with petrol is starting with the massive handicap to energy efficiency that is the petrol engine. At least a diesel has some chance of being efficient.
All that said, diesel and petrol are both duds in the long term. If we have cars in 100 years time then they will be electric - not hybrids but outright electric. And if we don't have electric cars then we'll all be catching trains, riding bicycles or walking.
As for the arguments about pollution from power stations, that's true but it's still a more efficient energy technology than petrol assuming we're talking about reasonably efficient power stations (and the ones we have in Australia are, with the notable exception of the older gas turbines and a couple of coal-fired plants, efficient enough in that context).
I'll stick with a conventional car for now but my mind is always open to new ideas.