I put 6000+ miles on a set of Schwalbe Marathons (moved them to a less used bike) and replaced them with wider and lighter set of Marathon Supremes and have had one flat in 5500 miles with those. I was really suprised when the front tire flatted and it turned out to be a tiny sliver of glass that had worked its way through.

The Supremes weight about 1 pound less per tire and the increased speed of the bike, for me, is a reasonable trade off.