A report on the de-funding of Hydrogen vehicles by the DOE brings a fresh breath of relief... if only it was accompanied by the defunding of the DOE, but I digress. Hydrogen power storage in general, and especially mobile hydrogen vehicles, is a ridiculous fantasy. Not technically - it is fairly straightforward. But it is extremely inefficient as an energy carrier, as Robert Zubrin put much more eloquently than I can in a New Atlantis article.
In terms of energy density, storage, and safety, hydrocarbons are the best thing around, at least chemically speaking. If and when it becomes reasonable to have renewable transportation fuel manufactured from primary energy, it will come in one of two forms: hydrocarbons derived from cash crops (ethanol, biodiesel), or hydrocarbon synfuels manufactured from water and atmospheric CO2. Hydrogen is a non-starter. I did my 6th grade science fair project on the hydrogen economy and predicted we'd all be taking 2 hour trips to Tokyo by now. I drank the Koolaid. But if you do the numbers, it just doesn't work out. Read Zubrin's article, it really lays the whole idea to waste beautifully.