When tuned to an XM radio station, under "Menu" there is a "Tag Song" command.
On p17 of the CUE Infortainment manual, under SiriusXM radio, this is detailed as
"Tag Song: Press the Tag Song button to tag the current artist and song information. When connected to iTunesŪ, the Synch button on iTunes may need to be pressed to transfer the song tags"
Having chosen this, it appears to Tag the artist and song title playing on the XM channel at that time.
However, now I keep getting a message stating
"IPOD MEMORY FULL - Your tagged song list will be transferred when space is available on your iPod."
1. The connected iPod has plenty of free space on it
2. There appears to be no way to delete the song tags, or even see what the tags are
Cadillac Helpdesk had no idea this menu item even existed, and were of no help whatsoever.
I did this same thing and had the same problem. I'm not entirely sure how I got rid of it... I'll try to remember but have you tried starting up the car without the iPod connected?
I've played around with it some more, and what appears to have worked is to disconnect the iPod over USB and iPhone 4S over bluetooth, and then connect only the iPhone 4S over USB. If I tag a song I still get an error message, but the general "iPOd memory full" message appears to have disappeared. Fingers crossed...