In Los Angeles, I used to get flats all the time. The breaking point was during an 8 mile ride where I got a front tire flat, walked to the nearest LBS to repair it, and got a back tire flat a few miles down the road (then having to walk the remaining miles)!! Two flats in one trip. Being new to cycling at the time I walked the next nearest LBS I came to and said "Please make this never happen again." They put something called "chubbies" in between my tire and tube and 4 years later I haven't gotten a flat since.

I can recommend them to all commuters. But, then again, everyone probably already knows about them. I was a fresh-faced novice to city ridin' back then.