I cant speak for *every* model, but I had a bluetooth, iPhone ready Kenwood head unit in my type-r and it was absolutely terrible.
I had two in the end as I took one back but they both appeared as broken as each other.
Random USB errors, 'ACCESSORY NOT SUPPORTED' errors on the iPhone, random disconnects and all sorts then iOS4 came out and it was even worse. I gave up in the end and just started using MP3 cds.
When I finally get around to sorting out a new system for the 172, kenwood will be right at the back of the list. It sounded good but it was absolutely useless for iPhone and iPod support.
I dont know if anyone has any experience of putting a stereo into a type-r but its probably the biggest pain in the backside in the world, so to say i was dissapointed is a bit of an understatement.