I find an _average_ of 40 hours to be quite extrem also. I've been at a new 40-hour job for 1 1/2 years now, after working 26/30 hours week for the 3 years prior. My impression is that 30 hours a week might be a realistic average to aim for (26 being the ideal amount IMO). It shifts the work-life balance to "I go to work and in the evenings and on weekends I do whatever I like", where 40 hr / week feels more like "life is work and I'm glad if I get one day completely off on the weekends"

EDIT: Maybe I should give some perspective: I'm single and under the impression that people in a relationship have an easier time managing 40hr weeks because they can better distribute the random shit that comes up every week (how people with kids do it though, I have no idea...). Also I'm currently laying in bed sick, due to having had no reasonable work-week for months, because the only thing I get as reward for finishing my projects in time and to the utmost satisfaction of our customers is even more work. /rant off I guess...