While I'm glad that President Bush has stopped pimping for Big Oil long enough to endorse hydrogen as an alternative energy strategy, I have to point out that hydrogen is not an energy source. How do you get hydrogen? Well, that's simple, you run electricity through water and collect the hydrogen, right? Then, you burn the hydrogen in your car. How much energy do you get from burning it? Less than you used to separate it from the water in the first place, quoth Wikipedia:
It is currently very difficult to obtain hydrogen gas without expending energy in the process. The process of splitting water into oxygen and hydrogen using electrolysis consumes large amounts of energy. It has been calculated that it takes 1.4 joules of electricity to produce 1 joule of hydrogen (Pimentel, 2002). If oil or gases are used to provide this energy, fossil fuels are consumed, forming pollution and nullifying the value of using a fuel cell. It would be more efficient to use fossil fuel directly
That said, I think hydrogen could be useful to power our cars, as long as we use nuclear, solar, or wind energy to get it from our water, with nuclear making the most sense. So now, to power our fleet of hydrogen cars, we just need a bunch of new nuclear plants, which most "green" activists won't abide. So now what?