Good news for one piece of hardware.
My Kenwood KDC-X696 works beautifully with an iPhone 4 (iOS 5 and iOS 6), iPad 3 (iOS 5), and iPhone 5 on iOS6.
This includes the USB jack via my USB to Lightning adapter and also by Bluetooth. Placing calls (from phone or stereo), receiving calls (from phone or stereo), looking up the address book on the stereo, Bluetooth audio for music (with track information and the head controls the playlist fine), music via the USB jack (controlled by the head) with track information, and other audio over USB or Bluetooth which includes map guidance by Apple's Maps and Navigon. It also charges over USB to the 30 pin adapter or the Lightning adapter.
I recently chose this stereo for an older car because Kenwood's site specifically lists it as compatible with iPhone 4 and iPhone 5 and iOS 6 over USB and Bluetooth. Some of Kenwood's stereos are listed as incompatible, and most of those are described as relying on Parrot for Bluetooth connectivity (The KDC-X696 is described on Kenwood's site as using their own firmware, not Parrot). I think that's an underlying theme with other manufacturers and car companies.
Anyway, I wish all of the stereos worked, but this one is working fine if anyone is looking for one that works as expected. Pioneer's site also lists which stereos are compatible, and I would like to assume it's accurate.