I quit coffee as part of New Year's resolution. I started feeling nauseous in the morning if I drank a cup of coffee in the afternoon the day before. Once I quit, I thought I'll be less productive, and that I won't be able to focus, but after a week or two, my body recovered from the caffeine addiction. I started drinking black tea - two cups per day. It's still caffeine, but in far less amount. I miss coffee, though…
Also quit coffee to switch exclusively to green tea. I was just getting too much anxiety. I definitely feel much calmer without coffee. In general for I think I was a great move, I work a little less, but when I work it tends to be on more relevant things.
I'll typically have one cup of coffee one day on the weekend, especially if I'm going to do something to burn the energy (hiking/biking).
EDIT: technically not a programmer but a grad student in a computational field, but I think it's very similar work mentally