1) Anyone who thinks that taxes have ANY purpose other than to pull in revenue is gullible. Honestly, I know you've been told by the media and your friends that it's there to modify behavior. But, er... no. It's there to tax you, and it will hide behind any reason. 2) How long do you honestly think it will be before they (OR.) will catch some criminals via this tracking system? Law enforcement will call it a "breakthrough" or "tool" or "revolution" in crime fighting. Since the system would is already in place... what honestly would you do to stop that abuse? 3) If there were long periods of time between uses of a vehicle... or you do something like fill up your 5 gallon gas tank for your lawn mower when you're at the pump. You'd most likely be investigated, or at minimum "red flagged" for odd behavior because you pumped more gas than your car requires for the millage you done. Thus (OR.) would have a reason to investigate you later if you were suspected of any illegal activities. Just some thoughts.
I think I like the large ice cube proposal better. http://en.wikipedia.org/wiki/Crimes_of_the_Hot