Now I don't need to drive anywhere. The poor folks who have to drive large distances to work are going to get screwed twice over: once at the pump (in terms of taxes), and every year when the gummint processes the GPS data. So much for buying a hybrid to save on gas! In the meantime, I will be paying the same amount to take public transportation. Enjoy being a slave to your automobile, folks.
And then of course, the security vs civil liberty problems. The government will be able to track to you to tax you, but the police will not be able to track you? Yeah right. Do you think criminals are stupid? Either they will tamper with the GPS, drive old beaters that don't have one, or they'll mug people on foot. It's just another way to keep ordinary folks in line.