One of the problems I have seen in most of the discussions from the hydrogen advocates is that they compare the supposed efficiency of a system that will be out in 10-20 years, with the average internal combustion engine today. I bet that by the time hydrogen is available, internal combustion engine efficiecny will probably have improved substantially, as I don't see fuel prices declining a whole lot long-term. That should create plenty of incentive for engineers to make more efficient engines. There are lots of things that can be done in 20 years in the way of heat capture, or more efficient engine cycles, to bring the efficiency of typical gasoline and diesel vehicles up. By then, once the fuel cells finally become avaialble, there will be much stiffer competition from the latest ICE/electric hybrids as far as efficiency is concerned.

I do however think there is potential in capturing the best of both worlds by having a plug-in hybrid with a large enough motor to run the vehicle alone, in a parallel setup with a small gasoline engine for longer-range travel (this could be unclutched most of the time for short-distance travel). Then only enough batteries woudl be needed for say ~15-20 miles one-way. That right there could eliminate about 60% in fuel/energy cost for most drivers, without sacrificing driving range, convenience, or performance due to weighing down the car with batteries for a full 200mile+ range.