The obvious question for us was whether Siri would work in a car when tethered over Bluetooth. The short answer: Yup.
When you hold down the iPhone's home button, Siri is essentially treated as an incoming phone call, fading out the audio and then playing the chime indicating it (she?) is ready for a command.
We tested Siri on a variety of vehicles, including two Mercedes-Benz products, a Chrysler 300, a Dodge Charger and a Nissan Maxima. The results were mixed, with some commands going through easily and others requiring a few attempts. Based on our experience, it seems that the mic placement and the level of cabin noise present make a predictable difference, and the Maxima we shot our video in tended to provide the best results. See for yourselves after the jump.