I have the BMW dealer installed ipod accessory in my 2004 330ci. As others have described, occasionally, the radio does not "see" the ipod. Rebooting the ipod always fixed this condition. The last time this happened, an ipod reboot did not help. It occurred to me to try to "reboot" the radio, which I was able to do by pulling and reinserting the appropriate fuses. Upon replacing the fuses, the radio recognized the ipod perfectly.
I would be interested in hearing of anyone elses experience with the ipod adapter in this regard.