The state of Massachusetts was (Governor Deval Patrick specifically) was talking for a while about a plan to embed GPS recievers into the safety inspection stickers so they could replace the gas tax with one based on how many miles you drive on state-owned roads. The recievers would track and store the information about every road you drove your car on, how far you went, how long you were stopped for, etc. and would dump that data into a computer via an RFID reader mounted in various street lights around the state, all you have to do is drive under one of these lights and suddenly the state knows everywhere your car has been for a week or so.
With OnStar, they don't start tracking your location until they have a reason, like that you pushed the button, or your airbags deployed, or they receive a request from a law enforcement agency, but with this system they would be constantly tracking your car and saving all of the data for "tax records" (amongst most likely other things since the wording in the bill was very vague in regards to who can access this data). Luckilly the bill was shot down, but it did get a disturbing number of votes.
