The facts of Kyllo remind me of the Simpsons episode in which Kent Brockman tells the viewers, "Of course, there's no way to see into the Simpson home without some kind of infrared heat-sensitive camera. So, let's turn it on."
I'd be much more offended to have the man tracking my behavior at home than in my car. Of course, I still object to the man tracking my vehicular movements.
I think that's what the Caballes Court is getting at when it refers to "intimate details" worthy of Fourth Amendment protection. Occasionally intimate details arise in a car, but the Court isn't too worried about protecting those.