Phil Windley's Mesh Networks and OnStar posts reminded me of a thought I had recently driving home from work. Wouldn't it be cool if "smart" cars could communicate with each other on current speeds, and this "mesh" could tell you when traffic slowed on the highway when it might be speeding back up.

Another idea would be cars communicating where they got gas at last (location) and at what price. So as your car got low on gas it could query the knowledgebase and see if there is a place near by with "lower" price gas.