If the US vehicle fleet could be plugged into the grid as generators, they could back up the entire world (for as long as their fuel held out).

Wow! That is impressive.
What a pity it could back it up only for half an hour.

What breaks grids is lack of spare capacity in an emergency. That's one of the things Poet was implying in his post. Distributed, non-central, spare capacity is the best form of hardened infrastructure you can have.

Another problem with grids tied to renewable energy is underutilization at peak periods where the energy simply cannot be used. If PHEVs become a means of storing this over production, then your need to build other expensive storage is reduced.

I know he was referring to peak load. Usually, half an hour would be sufficient. Besides supplying all of the electricity for half an hour, it could also supply the missing 10% of the electricity for 5 hours.

Or alternatively, I could chose not to connect to the grid, and in case of outage run my car as a generator for all of my house. And you bet that then I will really save the electricity, when I know that I have only a few hours worth of energy in the batteries, and I still want to drive somewhere.

Just the way he put the global numbers looked so enhusiastically, as if we could supply the world from our car batteries :-)))

I thought it was really funny.