I too am experiencing the same problem. Since I updated my phones to iOS 6 I am unable to view track information, or play/pause on my Pioneer AVH-P2400BT.
Strangely enough in my other car this morning which has a Pioneer DEH-P7100BT (a few years old) I was able to advance the track via the decks remote. The DEH-P7100BT does not display track information so I'm not able to test that feature, and the play/pause button is not intuitive enough that I ever remember where it is so I wasn't able to test that.
Later today I will test the play/pause functionality on the DEH-P7100BT and then try track advance on the AVH-P2400BT and report whether or not they work.
What pain we go through to be early adopters (and yet we never learn to wait...)