We don't have the thorn problem here...most of my p*******s are from glass. Usually it's brown beer bottle glass. From my very unscientific observation, I'd generally agree with the "slicks get fewer p*******s" theory. With a slick, if the invading culprit doesn't go through right away, then it's gone. A workmate with treaded tires seems to get more p*******s. I'm guessing that the tread picks up debris and carries it along, giving it more chances to get pounded through with each revolution. Anyone else want to weigh in with an alternate theory?