I just came across this concept today, and I must say that I am fascinated. I have felt what it feels like to be 'in the zone' - when you're completely concentrating on what you are doing. I have experienced this playing fast-paced games such as stamina-based music games or text scrollers, and studying a language. But I never even thought that it could apply to my programming life.

So towards that end, I would like to hear what experiences programmers here have had that helps towards fostering mental concentration and any positive experiences of programming 'in the zone'.