> In your example, attaching it to someone's car (presumably while at work, shopping, etc) it will follow them home and their iPhone would see that tag the entire trip until they get home at which point it would notify the tracked person.

Okay, but is that really different than driving down a random street, choosing a random house with a car in the driveway, and thus learning that that car parks at that address?

Knowing that the car you chose to put a tag on at the store later parked at a certain address is hardly that useful, isn't much easier than just following the car from the store one time, and presumably wouldn't upset most people because most people's security models don't rely on their home address being private and thus no one ever following their car home from the store.