Love my Schwable Marathon Supremes. I've had one flat in about 6000 miles, including 2200 miles of loaded touring. The one flat that I did have was caused by a 1/2 inch nail - it would have flatted a car tire.

Those tires were a bear to get on the first time, but when I had to deal with my flat the tire came off and went back on totally fine. I think they have to get stretched out a bit.

Still can't quite believe I've never had a flat on tour. Fire ants, broken cable and various other equipment screwups, but no flats.