batteries make good cap's :)
Batteries are better than fuel cells because they can keep the national grid charged at night. Any solar energy factored into the grid has to be backed up. At the moment this is by fossil or nuclear but in future this could be by cars at night. Fuel cells can't back up our green energy so we might as well go 100% nuclear if you are proposing fuel cells as a viable option. I don't think massive amounts of nuclear energy fueling a hydrogen economy is a bad thing. It just seems like a round-the-houses hugely inefficient way of doing something that could be alot easier.
@steogede: I think this could be benficial to the 'swap shops' if they finally become common place. They can offer more than one type of service. Want a newer battery, want one thats been tested to hold its charge well, want the latest most powerful super battery, its all there for them to sell to you. The shops will need to record part numbers and vehicles so that if you claim your 5 year old, 80'000 mile battery pack has just finished its first charge cycle and you would like a similarly new battery to replace it they can track you down and file suit. Much like driving off the forecourt without paying.
Nice points Daniel, it does seem like the battery manufacturers need to get in before the car producers so that the car producers are working to one standard.