they'll also know where we went. And for how long.
And don't tell me "That's insane, they won't do that!", because the natural progression of shit like this is to increase what they know about you and thus their opportunities to control you. I'm sure they'll have some 'reasonable'-sounding excuse for it, but sure as hell, they'll do it.
Actually, they'll do it without bothering to let people know about it first. And since this would require a federal database of all vehicles owned and by who so they can know exactly who to tax by the mile, it would be simple to add 'destination' into the tracking. Especially for people who are annoying them by calling this kind of crap what it is.