Sometimes you can go through periods of bad luck - in my two previous years of cycling I only experienced one flat.
This year is a different story however - I am now on my fourth tire since the beginning of the year (in all cases the tube and tire had to be replaced). Tire #3 I decided to get an expensive heavy-duty puncture-resistant tire and that lasted me about three weeks. Something managed to shred through it like a hot knife through butter. I went back to a standard tire and it has lasted me for the last 150 miles or so and counting (knock on wood).
In all cases where my tire burst I had to walk a few miles home which I am fine with. I don't carry any spare stuff for my basic commutes because the prospect of walking a few miles home doesn't really bother me.
Bicycling is still more than worth it though!