People who write software are using their creativity to solve problems. I compare it to writing using a very precise language and grammar to express a story to the user. I came across this video over at the 99%. In it Tony Schwartz, author of "The Way We're Working Isn't Working", relates athletic performance to creative performance. One thing athletes have known for years is that the rest between workouts is just as important as the workout itself. While it seems intuitive that it would work the same way with mental work, many creative professionals skip the rest part in order to squeeze in more work. This additional work is usually lower quality and eventually the lack of rest becomes detrimental to creativity.
(It's a flash player, so if you have flash block on click the whitespace below to make it load.)