I thought the main problem was that you'd be carrying around extremely flammable highly pressurized gas. Which can explode, and burns with an almost invisible flame...
Apparently the safety's got a lot better since the "explodes on collision" tests, though.
Transporting it as a gas is not feasible, and neither is transporting it under pressure. In order to get the distance you get from a regular gasoline fuel tank out of a hydrogen fuel tank you'd need an immensely big fuel tank. Not
impossibly big, but just very, very impractically big. The holy grail find a metallic lattice in which hydrogen can be "stored", and then routinely added and removed.
My university professor in inorganic chemistry is one of the leading scientists on the field of hydrogen storage, and he's constantly bickering about how damn easy gasoline is (it's "free energy: we just dig it up and there it is".), making the switch to hydrogen power almost impossible. Any step in order to make hydrogen vehicles resemble the ease of gasoline vehicles ends up with a single large flaw. For instance, some lattices contain a lot of hydrogen, are easy to manufacture and can be filled/emptied in relatively convenient timeframes, but the weight of the metals make it infeasible as a whole. Others may look similar, overcoming the weight issue but replacing it with a refuelling issue, requiring several hours of recharge in order to fill up a small amount. So far the holy grail hasn't been found yet, and that's probably the main reason why hydrogen vehicles aren't really amounting to anything but PR stunts.