Interesting reading. I did a forum search on Bluetooth as I've just taken delivery of a new car that has bluetooth built in to the SatNav/Computer/Audio Player. I don't think it's worked since I got it. I can connect and pair my Ativ S fine, but then it seems to display various states on the phone, such as "Connected - Audio", "Connected - Headset", or just "Connected". Most of the time if I try and make a call it connects ok (both the phone and in-car display show the call as connected) but I get no audio output. My phone doesn't lock up as in the OP's case, but it's clearly flakey. I had wondered whether it's a fault with my car's audio unit, but my iPhone works fine.
It's certainly frustrating when, for all of the great features of WP, there are some niggles which have the potential to be deal breakers when it comes to every day use.