After having trouble with flats, I first put a pair of Specialized Armadillo kevlar-lined tires on my bike in December 2008. They worked well -- I only got one flat while they were on my bike -- but after about 18 months, they started getting bald patches where the tread separated from the kevlar lining.
I got another pair of Armadillos in May 2010, and I've only had one flat since then. But earlier this week I heard a thwap-thwap-thwap on my ride home. Turned out the tread had started peel off:
And that's after only about 15 months this time. While I would estimate that I put on about 3,000 to 4,000 miles per year, that still seems like an unacceptably short life for a bike tire. So I've replaced my rear tire with a 700x32 Michelin City. I'll let you know how it works out.