I've gotten easily 30 times as many rear flats as front flats. When I flat up front, it's usually pretty spectacular circumstances, too. I had a really nice Tufo tubular clincher up front for a while until a drainage grate that came out of the darkness tried to kill me. I managed to stay on the bike while my front wheel went into and came out of a long opening about the same width as my rim. Shredded the sidewall for 18" on both sides. The other times I've flatted up front have all either come from the front edges of really nasty potholes or from pinching the tube one way or another while mounting *****-ass 19mm tires that I have to run up front to clear my fork crown.