I've been using Navigon since I read on this forum and its great, For the price and how well it works with the only thing I can compare it to was my old C550 Garmin unit. I found the the software working with the 3g gps to be spot on right now to the meter. And all I did was use the ipod cable from my radio and listen to where I have to turn. There was no need to watch it while driving.
The bad: (not really, I just miss some features)
-load times : and be a bit slow, don't know if this is the software waiting for a GPS signal ?
- You can't load your own way points , the only thing I miss from using my old garmin, great for known "polica" hang outs
esp when your in a city you don't known all too well.
- lack of traffic/delay data, there must be some way, but maybe I'm asking to much
and that's all I have to say , its great piece of software for the iphone.