I hope the whole PUMA thing gets beyond the concept vehicle stage. Personally I think my wife and I could drop down to one car if we had one of those. Maybe we could have two PUMAs and one car and then only drive the car when absolutely needed. Their ability to drive in trains could be the beginning of the personalized pod transportation I've been hearing about for years, too.
People with kids might feel differently about dropping to one car, but maybe even some families might go for it. Everything that can get some of us off fossil fuel is a great step. I think this could be a bigger change than the regular Segway, if they make the effort to move forward. I know that many past concept vehicles, particularly the environmental ones, were just greenwashing attempts to claim future technology trumped the need for present-day regulation. Hopefully this will be different.
UPDATE: in a related climate issue, I just saw this note about Obama possibly backing off on 100% auctions of carbon allowances, which would be a big mistake, as Drum says. I think there's a way to do less than 100% auctions without making the public subsidize the polluters, though: make the free allowances non-transferable. You lose the market efficiency from selling allowances, but I think it's politically more viable. I've never heard anyone suggest it, though.