First of all, my car, an inexpensive 2004 Corolla, has a 12v power connector inside the center arm rest. I also discovered that it has a recessed lip so that cables can come out of the arm rest without getting squashed. Good thinking, Toyota. So I plugged in the power supply there. Stephanie bought me an iGrip sticky thing to put on the dash, so I just plop the thing up there with the iTrip in it. It's so iDeal. ;)
Anyway, getting it to work well was not without its quirks. There really isn't any empty spectrum in Cleveland, not even in the non-commercial band. So to really get a clear signal, I had to remove the antenna off my car (it unscrews). Not a big deal, since I never listen to broadcast radio anyway. That allowed the iTrip to get a signal into the radio without a lot of interference.
Getting good quality wasn't instant. First off, the transmitter takes a minute or two to warm up. It's like my college radio days where you turned on the tube to warm it up ten or fifteen minutes before you started to broadcast. Lots of noise until it really starts to go at full strength.
The other trick is getting the volume to a good spot. Even though the directions say the unit will compensate, I found that it's really sensitive to over-modulation. It also doesn't put out quite the volume that broadcast does. Setting the volume to about two-thirds works.
Finally, you have to set the iPod's EQ to the treble boost setting. That makes it totally adequate. There's still a little FM noise, but you can only hear it during silence maybe stopped at a light. There's too much noise in the car to worry much about it. It wouldn't be good for home use, but it works great in the car.