(sorry to jump in late to this discussion) fuel cells have immense problems. All of what I've read indicates that this is a huge red herring
- there's no infrastructure for hydrogen. Yes, you can use any hydrocarbon, but then you're not getting all the benefits of the fuel cell
- there fuel cell technology is nowhere near reaching practicality
- production of hydrogen is energy expensive
On the topic of this discussion, there's been alot of talk on plug-in vehicles and their limited range. The current thinking is that you'd make the plug-in vehicle a "super hybrid". As noted, the Prius Plus is like that. You make the batter pack larger and plug it in overnight. That might give you a run-time of 50 miles. Enough for most shopping trips and commuting one way. Then you plug in at work for the commute home.
However, the great thing about the Plus is that it's still got the fuel engine so you don't have to worry about limited range. If you drain down the batteries, then you're back on the conventional engine and no worse off than a normal hybrid except for an extra hundred pounds of batteries.
The problem I see with this is as mentioned by another poster - energy transmission losses. Currently, with our large electric grid, the transmission losses average 7.2%
Note that the national goal is what they're calling the 500 mpg car. That's a mainly plug-in hybrid electric that gets an effective 500 mpg.