I have a 2012 VW Jetta SE sedan & an iPhone 4, and formerly was able to stream music with no problems, good sound, and had control via my steering wheel to go forward or backwards with the songs.
Not so much with the iOS 6 update. Music quality is lower, and while I can get it to play & still control volume, I can NOT control forward/back with the steering wheel controls - I have to use the phone itself. I am NOT happy with this.
This describes my situation perfectly. I've got a Kenwood DNX6190HD which, until iOS 6, worked perfectly with my iPhone 4S. The iPod cable connection still works as expected. I have also been able to stream w/ control using my Blackberry Bold 9170 (work phone but it has Bluetooth-connected Pandora and someone else pays the bill so...