Within the past 9 months I put Marathon Plusses on both of my bikes. I have not had one flat in that time. I commute daily at least 5 miles, often much more. I would guess I'm doing around 100 miles a week = 400 miles a month = 1,600 miles with one flat. That's the first time I crunched the numbers. That ain't half bad. I haven't seen any signs that the tires are getting worn, either, but then I have two bikes, so one is always "resting."

I agree with Andy K. You have to make your trades. I'm not a speedy rider, and both of my bikes have hub gears, meaning no quick release tires. I'd much rather have a little extra weight than to have to deal with changing a flat on the road, so I went for the toughest tires I know of.