They'd have to work it so that it would limit you to the speed limit you're travelling through at the time, which means GPS - ie they'll know exactly where you are. Now I like to feel that i drive within the law and I have nothing to fear from the law otherwise... but i don't think I'd be comfortable knowing that someone knows precisely where I am all the time, without me telling them myself.

This would also happen if they brought inthe pay per mile scheme - that could easily be used to limit speed, as the GPS system would HAVE to be used for billing purposes.