Success!
Okay, at least partially. The GMPD2 does play songs from my iPod Nano, and I can control it from the steering wheel. It displays the playlists, as far as I can tell (I'm not fully loaded yet with playlists), but does NOT display the title or artist on the HU, but that might be a function of the MP3 songs that I have loaded so far. I'm new to the iPod, so I'm still loading songs and setting up playlists.
In my car, 06 GXP with the Monsoon and factory XM player, my iPod is mounted in the trunk, in the left wheel well with the XM unit. It plugs into the XM radio there, so the iPod stays in the trunk, out of sight and harm's way. I also had to buy a small plug that goes between their cable and the iPod to charge the iPod, clled the Scosche passPORT Charging Adapter for iPod touch 2G, 3G; iPod nano 4G; iPhone 3G (Black). The total for both this and the harness, with 2 day shipping (I ordered it from Amazon late MOnday night, got it Wednesday), was $168.58. iPod was another $150. A little pricey, but considering how long it would take to install a new head, and work out all the little details, etc., a small price to pay. I have more money than time right now, so I don't might it.
I was trying to get a second-generation iPod Classic (30 GB) to work, but the harness wasn't made for that unit. Bummer. Could have had a lot more songs for a lot less cash outlay, as the old iPod was free from a friend.
EDIT:
I get the display of songs when I press the center of the TUNE knob. I was having trouble switching off of the current playlist, but I unplugged and plugged the iPod back in and it seems to be okay.