This excellent post on BNET by Margaret Hefferman asserts what some of us have been saying for a while – that there are limits to our working hours beyond which we start to become less productive. I noticed this in the 1980s when working for my first employer, a strategy consulting house with a bizarre over-the-top work ethic. We were contracted to work 50 hour weeks but the norm was to do much more with many people in the office late at night and through the weekend. I noticed at the time that every hour above the 50 was increasingly likely to produce a mistake of some sort that would take me ages to correct later…