i use the dvd-r/w drive(I want to say it is a panasonic?) from the mp3car store, and have not had any problems with playback/skipping/scraping "it just works"
The one I bought doesnt seem to like much vibration at ALL. I hooked it up to my desktop before we decided to begin mounting/molding in the car and I can hear the disc "scraping" when I move it up/down, tilting, etc.
What drive do you use? Does yours hold the disc securely? Do you have any type of skipping issues in the car?