I havent used the usb playback often but i have been using iphone 3gs plugged permanently as mp3 player. It has been working well except for the occasional hickup where it will not pick up the iphone after starting the car.. To me this doesnt sound like the same issue. I just have to replug the iphone to get it to work.

I'd say check your version first. My gps unit hasnt crashed once since.

Cheers