The problem with hydrogen fuel cell cars is primarily one of efficiency. Hydrogen fuel cells work by more or less turning hydrogen into electricity but it takes quite a bit of electricity to create the hydrogen in the first place via electrolysis and then you loose more energy in the hydrogen to electricity conversion process. Its a lot more efficient to just store the electricity in a battery. The only upside to hydrogen fuel cells is quick refueling, but the costs involved due to inefficiency will pretty much always make it too expensive. At least until we start mining it from asteroids, pulling it directly from stars, or just scooping interstellar hydrogen up with magnetic fields (see Larry Niven for that one).