I have only had one flat over the last 5000 miles of (road) riding. It was a front tire blow off while I was crossing the street during a local century, and when I looked at the tube there was a long tear along one side of the tube. I suspect that it was because the bike shop I had put the tire on pinched the tube between the tire and the rim (exactly the reason I had them do it instead of doing it myself).

I think the things you can do to avoid a flat are,
1.make sure that your tires are inflated to the max PSI,
2. Make sure that the tube is seated well inside the tire, and not between the tire and the rim.

Of course road debris (etc.) changes the equation a bit, and I think offroad is a different story. Offroad I run the lowest reccomended tire pressure, because the ground around here tends to be wet. I have only pinch flatted with off road tires once, and that was because I hit a curb pretty hard on part of commute to work (the majority of which is offroad).

Sorry about the long winded response.