I used a 3M kit on the headlights today. The passenger's side was horrible while the driver's side was "normal" looking. I'm a bit puzzled as the car only had 17,500 miles on it when I bought it and for the past year it's been in a garage except when it's being driven.

Anyway, the 3M kit did a beautiful job. It brought both units back to factory clarity. Not bad for $25. After going through the process, I'd advise using a kit that includes a drill. I can't imagine doing that amount of abrasion by hand.