Okay, so this will probably get me branded as a member of the foil-hat crowd, but I'm getting concerned about the amount of surveillance we're under in our cars. I'm not quite to the point where I think it's Alberto Gonzales' idea (I'd be REALLY worried if that were the case!) It just seems like more and more little things are coming together to allow someone to forensically build a pretty good picture of what's been going on in your car.
Many cars today have a "black box" that records many different types of events. Since car manufacturers are still using older, stable technology, there's not a tremendous amount of storage in these boxes so they're not keeping a running account of your driving (yet), they're just recording major events. Basically any car with an airbag has some form of event data recorder, and it's likely that every new generation will be more capable and store data on more events and over a longer period of time.
Some readers are thinking "But I have nothing to hide, why should I care about this?" Well, let's take as an example a minor fender-bender. You are convinced that the other driver is completely at fault because he failed to yield when he pulled into the major road from a side road, and you're sure your insurance rate is safe. How happy will you be when his (or his insurance company's) lawyer subpoenas the data from your car's black box and shows that you contributed to the collision because you were driving 5 mph over the speed limit?
I think the best hope for keeping manufacturers from putting all sorts of collectible data that's not necessarily pertinent to maintenance and service will come from my least-favorite source, a lawsuit (or fear of a lawsuit.) If the manufacturer feels that collecting unnecessary data within every customer's is a potential liability, they'll think twice before collecting it "just because they can."