I had a flat last Friday with the rear tire on my commuting bike. Over the weekend, I purchased 700×28 Continental Ultra Gatorskins which have a tough belt and sidewalls to replace my 700×25 Michelin Carbons. The ride seems a little bit stiffer, but the tires should be more resistant to thorns and glass. Examining my rear Michelin Carbon that went flat, it looks like it was just a little piece of broken glass which penetrated the tire.