Just to clarify, there has been a lot of technology advancements in fuel cell technology in the past 20 years.  These engines require Hydrogen and Oxygen to be stored separately. Right now that requires a "gas" tank that can withstand about 5000 pounds per square inch of pressure - something that can be done for spacecraft, but to date, not mass produced, but we are getting close. I am on a waiting list to drive a GM fuel cell vehicle when they are available - probably in 2009. The technology is available. The challenge is making them safe. In an accident, the high pressure containers are like bombs. Once that issue is solved we should see some dramatic changes.

BTW, one other thing. It takes a lot of energy to breakdown water to combustable fragments, so most of the automobile technology assumes liquid hydrogen and liquid oxygen becomes more readily available. Building that infrastructure will take some investment, too. [Unlike space vehicles that can sit, take in sun energy, convert water and store the components.]

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