Before I started using Mr. Tuffy liners, I was getting a flat a week at least, sometimes a couple a week. Since then, I get about 1 a month, if that. I've only had 2 punctures that the liners didn't stop in about 6 months. One was a 2" finishing nail... that would have gone through any tire.

EDIT: The other couple of flats I had were from tube failure, not punctures. Even a "tough" tire will pinch flat if you let it get low and hit a pothole.