Are fucking stupid. Don't mean to hate, but let me show you why they are not useful AT ALL.
Ok, lets start at the first point - efficiency. Hydrogen and oxygen gas are produced through the electrolysis of water. This separates the raw elements from the water and requires energy. Now wait, most of you would assume this, no? The energy produced from burning the oxyhydrogen gas produced from electrolysis is LESS than the energy used. Did you get that? If I made a fuel cell powered by a car battery and used the gas produced by that battery I would waste more energy than just running the car on the battery.
Second point that is normally overlooked. I have heard time and time again that "This 'new' hydrogen fuel cell technology will reduce or eliminate our dependence on fossil fuels."... WHAT? Look past the fact that hydrogen is more wasteful than using electric alone. We still need to get the energy for the electrolysis cell... Where's that going to come from? Sure, nuclear power is helpful, but we can't rely only on that. You know what will happen? We will be burning coal and oil to power this new, wasteful, expensive shit. Which leads me into my third point...
Helping the environment. It is true that burning hydrogen and oxygen produces only h2o as a byproduct. This is amazing but not useful. As I said before, we will continue to burn fossil fuels to power the electrolysis cells. Now say you get the electricity from solar or nuclear power. Why waste the extra electricity? Why not just run your car on that?
So what do I suggest we do? I'm a libertarian and believe that it is not the governments responsibility to solve this problem, but I also believe that global warming as rising fuel costs are very real problems. You should ALL watch the documentary who killed the electric car
http://en.wikipedia.org/...lled_the_Electric_Car%3FTo be honest, I'm not 100% sure what the best choice is but it is MOST CERTAINLY not hydrogen technology. Thanks, live green, live safe.