My car had some "old dog face" going on when I got it so I tried Dr. ColorChip, which overall worked pretty well. Small rock chips and the sandblasted-road rash kind of surfaces came out better than any big chips or scratches, but I think they mention that on their site. Here's a before and after of my car, sorry about the crappy pics:
http://www.flickr.com/photos/1233217...7624538625495/