I've only been commuting for about a month and have had 5 flats on my stock Kendra tires. Last week I put a mapping GPS on my bike and marked every fleck of glass I saw in route. Yesterday, I spent 8 hours with a leaf blower cleaning up problem spots on the trails and places that glass congregate in the the voids (road debris) between the two bike trails I use going to and from work. I also ordered a pair of Continental Ultra Gatorskins. These two things, and learning the circumstances, here, where glass accumulates in the road, should help reduce flats greatly, I hope I hope. Still, I've determined that there will always be a 150 foot stretch between the two trail junctions where I will always have to carry my bike through.
The Kenda Kourier's that came on my low-end bike were the absolute WORST. I am much happier with my Specialized Nimbus on the new bike. They aren't bombproof, but I have yet to have an issue.