Missed the point...
Where we are right now, hydrogen is as (brown - as an opposite to green?) as burning fossil fuels. All this energy density stuff is really aside from the point too. The biggest reason all cars produced for last ten years haven't run off hydrogen is the creation/storage/transportation. We have H2 fuel cells and they work fine, we have highly efficient electric motors, but for powering the fuel cell there are two choices - buy bulk H2 at stations or manufacture it on the fly.
As for large scale liberation, electrolysis is too inefficient and the current method is, as pointed out above, still dependent on fossils and as brown as regular engines. We are researching this.
There are a ton of on the fly methods also being researched at the moment, but IMO this idea from Honda is a good one - if they can sell the home stations with it. It shouldn't flub the way the first poster said their last one did, H2 isn't available, regular gas is. If I could make H2 in my garage with a station and fill my car as needed that would be great. My gas bill would go up but I would save money on petrol. Presumably I could fill up at H2 stations also if I wished. It would probably cost about the same but it would be more convenient to me and when they find a way to produce H2 efficiently, I'd be ready. hydrogen is the best replacement we know about. Nukes under every hood? Hardly? Run everything from charged batteries? Just as silly. Hydrogen fuel cell tech is already here, used, reliable, ect. the problem with it is "How do we get hydrogen without starting with fossil fuels?"
As far as hydrogen infrastructure not being there, do you guys think it is there for everyone to be charging their cars every night? Yeah right, the source and lines would have to be tripled, at the least. And how do we produce that much electricity? Not without the same dependency on fossil fuels, and wind/solar/hydro/geothermal power on that scale is still a dream. Aside from fusion (which is still a pipe dream) hydrogen is the best route to go.