Hydrogen powered cars are on the road *TODAY*.
That being said it will take a long time be practical, but it holds a lot of promise for large scale application. Why ?
Simple, there is a lot of money in the gasoline business, and in the long term the oil companies and governments (tin foil hats on please) will need something to replace their revenue streams with, and hydrogen is the closest they can get to that. The govt' likes it too because it has the same kind of taxing possibilities. Airlines like it because the powerdensity is comparable and so on.
Possibly there are other major reasons for this push.
One way or the other, hydrogen probably will happen, and it probably will happen fairly soon (within 20 years on a large scale according to most experts, sorry no links for that but I can dig them up if it is desired).
As to the myth of hydrogen being clean:
Hydrogen is NOT a fuel. It's a storage device. You have to *make* hydrogen first, and how you produce it is a much bigger factor in determining whether that particular batch of hydrogen is clean. The combustion of hydrogen (2H + O -> H2O) is obviously cleaner than the combustion of carbon based fuels.
Say you use a windmill or solar bank to power a hydrogen splitter, take the hydrogen with you in your fuel-cell+electric motor powered vehicle, then that is 'clean'.
Otoh if you buy your hydrogen from the corner gas station and say 'Shell' or 'Esso' produced it using natural gas to meet demand then that's almost as bad as burning gasoline directly.
This is exacly the reason why big oil would far prefer hydrogen to other technologies, essentially a 'seamless' path from their point of view between the current situation and the hydrogen economy. Evolution rather than revolution, and that is - on a global scale - probably the best for everyone. A revolution would probably be driven by a global oil shortage and that would nottg be a pretty picture.
The myths are that hydrogen is hard to produce, impossible to hane (not true, partially true), unsafe (so is my pocket knife, it's all about following procedures). Someone on this remarked that making and storing hydrogen in useable quantities is outside of the 'home experimenters' capability.
I suggest you speak for yourself I think that basic fuel cell technology is within reach of the amateur, and if you live long enough to get to the level where you can pull off that kind of thing you'll probably live to tell about it.
Fuel cell technology is being patented left right and center at the moment, everybody wants a slice of that pie (Ballard, Daimler-Chrysler, Shell and probably lots of others) are investing unbelievable amounts of money in order to get some kind of lock in.
In the long run, don't be surprised if producing 'hydrogen' privately is outlawed (some convenient explosion somewhere as the excuse) just so you won't be able to avoid taxation. If you think that is crazy then check your local laws wrt distilling your own alcohol. 10 to one it's illegal. Just like it will possibly be illegal one day to have a windmill. And if you don't believe that, there are already areas where you are not allowed to own or operate one.
The fuel craze is all about 'control', and the price we pay for our mobility is in a large part diverted towards taxes and oil company revenues (a few percent mr. Cheney hah ! I should know, but that's another story). The gas stations make pennies per liter, the governement roughly 35%, the oil companies take the rest and their bookkeeping is pretty murky, even though they are public companies.