An article (subscription required) in this week's Science discusses hydrogen fuel use for transportation and whether it makes sense for us to concentrate on hydrogen now as a replacement for fossil fuels due to global warming, air quality, and energy security concerns.
In short, David W. Keith (CMU) and Alexander E. Farrell (UCB) (authors of the article) argue that it is too early to concentrate so much on hydrogen's promise and instead we should be pursuing hydrogen while also working within our current systems to address these issues.
For each of the areas, the two lay out alternatives that might move to resolutions of these three issues faster and provide a better holding pattern while waiting for hydrogen to achieve its true potential.
For climate change, they suggest continuing to increase the fuel-efficiency standards for vehicles (although they don't mention the CAFE standards, they are the only existing US metric of this kind).
For air pollution, they suggest more of the same, but also determine that the cost per ton of removing pollutants from emissions by converting to hydrogen will be about $1 million, in comparison with current-day standards of around $2000 per ton in the coal industry and others.
Finally, for energy security, they suggest continuing the pursuit of biomass and and other synthetic hydrocarbon fuels.
It's an interesting take and there is certainly a lot of cited evidence. Although I'm rather fond of hydrogen in concept, I like the dual approach, which gets us further in the short run, but there in the long run.