Not just storing it safely, theres also the problem of creating the hydrogen such that it makes sense to move away from oil. Methods used commercially to produce hydrogen are really inefficient and expensive right now. They either create the same amount of emissions as, or more than, their petroleum equivalents either because of the massive amounts of electricity(from our aging coal fired plants..) they consume, or simply because it is a by-product of the chemical reactions used.
Not that im against hydrogen cell cars, I just think all these hurdles to put hydrogen cells into practical use stem from the lack of commitment and funding to research and development from governments and corporations. Aerospace and IT technology has improved by leaps and bounds yet cars are still using the same combustion engine invented in prehistoric ages. Yea we invented EFI, variable valve technology and cylinders that switch off when not required... but its still burning fuel pushing our pistons...
We've seen prototype fuel cell/electric cars from so many manufacturers for ages.. I think whats been lacking is the economical and political will to go in that direction..