This is a great post from 37signals on work hours. The comments are just as interesting as the post. There are still a lot of places that would flatly reject any notion of flexible time or shorter work weeks, and that's a bummer.
I suspect I'd be much happier in a four-day week, and in fact I'd even take a pay cut to have it. From the work end, yeah, I'm only productive 25-30 hours at most per week. From the life side, having an extra day a week for me makes me far more likely to clean the house, read, buy groceries or otherwise function in the context of my life in ways I don't currently. I know this from my consulting days, where I never scheduled stuff one day a week, and felt immensely better for it. I lost weight, got my head together and generally felt better despite the difficulty I was having at the time with the separation.
What I find even more unfortunate is all of the people who simply adhere to the way things are with total acceptance. The industrial revolution ended a long time ago. We're not a nation of worker bees on an assembly line, and we become more and more self-aware about what life is supposed to be about. The problem is that the culture is driven by a minority who can't get up to the roof (in the "follow your bliss" Blue Man sense), and we can get stuck working for those people. I've met countless people who do what I do that find it staggering that I don't work 50 hours a week.