I ride in NYC too, and I'd say I've been averaging about two flats a year. They were more infrequent when I was riding Gatorskins. Now I ride Jack Brown Greens. It's really not so bad because I do always carry a patch kit and a pump, and I can usually get back on the road in 5 minutes.

Fixing a flat is a good skill to learn because I've found that other NYC cyclists are often inhuman monsters. While I've stopped to help others fix their flats, I've never had anyone do so for me. Once I got a flat on Prince St during the morning rush hour, and all I needed was a new tube of glue because mine had dried out, and I could not flag down any cyclists at all in 20 minutes. Most people just rode by ignoring me as I asked them whether they had a patch kit.