I just bought my GTI a couple weeks ago. I had a Neo iOn (which was a rebranded Peripheral Electronics iPod interface) in my old car (Audi A4 Avant) which I moved to the GTI. The audio input worked, but the controls didn't, so I contacted Neo (
http://www.mp3yourcar.com) and they sent me a new unit, which turns out to be a rebranded DICE interface, which works great. The radio & steering wheel controls work as advertised. I ran the cable into the glovebox. It's not long enough to make it back to the center console with enough slack to be useful, so in the glovebox it stays.
The installation was pretty straightforward thanks to all the info about disassembling the center stack I found on the net. I moved the satellite radio wires to the new plug so that still works as well. Disassembling the dash is annoying. I popped 4 of the clips off the lower dash faceplate. I used epoxy to reattach them - they'll probably stay on better now. But what a pain.
The radio displays accurate elapsed time & track number information, but does not display track name/artist information. I assume this is a limitation with the stock stereo (I have the Panasonic Premium 7 stock head unit). I read somewhere on the net that DICE was planning an interface cable that uses the satellite input on the radio so that the radio will display track name/artist information. And since the interface has an auxiliary input, supposedly you'll still be able to use satellite radio but switching to the aux input. I'm not sure if this is a big enough win for me to tear the dash apart again. I'd like to get track name/artist information, but for me, the biggest problem is controlling the iPod from the car stereo controls. It's just too hard to navigate 40 GB of music with a couple buttons, even if you can see what's playing. And even though the DICE unit is better, you still can't navigate by artist, which is usually what I do.
The Harman Kardon Drive+Play looks promising. I just wish there was less "stuff" to install. Really what I want is for VW to give me a multifunction "jog wheel" that rocks forward/back/left/right (a jog-wheel-click-wheel hybrid, if you will) right in front of the gear shift on the center console that I can use for anything (including navigating my iPod) and for the iPod display to me mirrored on the head unit display and in the trip computer area if I'm in audio mode.