I love my SYNC so much that I hate having to drive any other car for an extended period of time, including the Mercedes I work on. The only issues I have ever had with my system is the occasion after parking where the audio will default to Bluetooth Media instead of the USP IPod I had just been listening to before I got out of the car.
Other than that there is nothing I can fault the system for. I can use voice commands on the highway with the windows down, I can make crystal clear phone calls without having to pair my phone everytime I get in the car(hint hint Mercedes), I can run my IPod on long road trips without having to take my hands off the wheel.
For the IT guys who understand it better than me, I can still understand enough that making a system compatible with hardware from different manufacturers is a daunting task.
Moreover, perhaps there are a few people who might have actual faulty components in their vehicle that can be fixed?