I'm happy with my setup at the moment because it works really well when getting in and out of the car multiple times. The audio is stopped when turning off the car and started up again when starting up the car. The best part is that because it's hard wired via the ipod adapter cable there is no lag time associated with bluetooth reconnection. The trick I have to use however is to set the receiver in video mode and then select which media to play on the phone itself. After that the play and pause buttons on the receiver do control the playback on the iphone4. This is the only way the play and pause commands work properly with third party apps (eg. downcast / other podcasting apps).
However, if I were to ever upgrade my receiver I'm afraid I won't be able to get this setup to work again. I doubt I'll be able to use screen mirroring because the iphone4 is too old for that (old style ipod connector) and most usb connections control only the built in music player of the iphone4, not third party apps.
Does anybody have experience with using the newer pioneer av units with and iphone4 as a media player ?