I have a problem with that item for a slightly different reason -- my own experience and an increasing amount of published research shows that slacking off a fair amount is actually productive.

I rarely have breakthrough "A-Ha!" insights into thorny code problems I'm working on while sitting in front a computer actually thinking about the problem but I have them quite often when out on a long walk being "unproductive" and not even consciously thinking about the problem. Once a problem reaches 3 or 4 levels of indirection my subconscious is way better than my conscious brain at solving the problem in an elegant way and I choose to "slack off" daily in order to take advantage of that.