The only problem I foresee with hydrogen fuel cells is that to "fill up" you just put in water, correct? Well then what is going to happen when we all fill up with water, we already have a fresh water shortage, and then were going to be interrupting the water cycle on a huge scale, and we will never be able to get that water back naturally, because once you separate the hydrogen from the oxygen then the molecules never get back together because you have used up the hydrogen molecules and transformed them into energy. Now I don't know about you, but I'd rather have fresh water then get the car going, just get a bike...

Come on guys, we have the smartest scientists in the world working on this and no one has thought of this, I'm in 8th grade and I figured this out.