Overwork and productivity

I've been realizing that I have to do better at defining boundaries between work and play - or at least different levels of work/play to avoid burnout (New Yorker via GTD):

The perplexing thing about the cult of overwork is that, as we’ve known for a while, long hours diminish both productivity and quality. Among industrial workers, overtime raises the rate of mistakes and safety mishaps; likewise, for knowledge workers fatigue and sleep-deprivation make it hard to perform at a high cognitive level. As Solomon put it, past a certain point overworked people become “less efficient and less effective.” And the effects are cumulative. The bankers Michel studied started to break down in their fourth year on the job. They suffered from depression, anxiety, and immune-system problems, and performance reviews showed that their creativity and judgment declined.