On the surface, not a bad idea. But this would require that every driver have a unique set of keys. This is not how some car owners (e.g., parents) want things to work.

But if there were a user PIN or some other recognition aid that conveyed that ID information to the car's computer, we're onto something.

Now with the likes of OnStar, there could probably be a mechanism by which the primiary driver/owner was able to put out as many "keys" to the vehicle as necessary, and allow programming to determine who's key worked at any given moment (e.g., the kids' are disabled, but the valet key's enabled). It could be a real pain to manage, but one way could be via profiles, stored and transmitted va PDA or Blackberry.

You'd never have to worry about car thieves again. Unless you want to consider the dreadful and ridiculous scenario of a carjacker jumping into your passenger seat at a light. Ha ha, you think, and turn off the ignition. He beats on you until you agree to give him the PIN to start your car. He drives you to a bank, where he beats on you until you agree to give him the PIN to clean out your checking account. At some point, he throws you out of the car becuase your security scheme is just too damned annoying!

I believe new BMW cars have the ability to save the settings of different drivers (like chair positions, mirror positions, etc) and a friend of mine who has one has been very pleased.

Maybe speed but if it does the time then kids cars could just stop on the high way if there time is up.

Yeah, timed sessions seem like a bad idea. Someone with privileges would have to drive out to get the car moving again. In its place, a GPS system showing the location of the car to registered owners, activated when certain drivers are using the vehicle, could be useful.