I agree with Riggz. Grom had a good idea, but implemented it poorly. I'm getting more and more static now in my songs. Their issue is their flimsy connections on the actual units. I've had two of them, both had the problem.
How much did this cost? I prefer the ease of a USB drive, but I guess I could use my HTC EVO to store my music and just control it from that. How long are the cables once you've run them to the right spots? Can you pick your device up high enough in front of you to see the road? Or do the steering wheel controls work (that would be awesome!)? How much?
Also, I'm stickying this in the FAQ thread. I might expand on your HowTo if I decide to get this (pending the answers you give me to the questions above).