<sssiiiggghhhh>
Time to get out the physics book again...
It's easy to get hydrogen out of water. But the power you get out of the hydrogen is *less* than the electricity you used to get it. Looking for some science fun? All you need are a couple batteries, some paper clips and some salt water:
http://www.theodoregray.com/PeriodicTable/Stories/001.1/
Another way to look at it: Petroleum is an "energy source"; we get more out of the gasoline (or whatever) than we put into drilling/refining/everything else we do to get it.
Hydrogen is (based on currently available technology) only an "energy form"; perhaps a convenient way to store or use energy, but it depends on an energy source being available to produce it.
Until this fundamental issue is resolved, developing fuel cell cars on a large scale simply won't make sense. Either we come up with a more efficient way to procedure hydrogen, or we come up with some other energy source so plentiful that any efficiency loss converting it to hydrogen isn't important.
