A colleague in a former workplace tried to quit and was persuaded to stay by the offer of a four day week on the same salary (talented guy, difficult and expensive to replace). From what I could tell the result was that he was highly motivated, continued to be very productive and of course was much happier. I think he took Mondays off, and would use the extra day to go on longer trips at the weekend (often surfing iirc) that he wouldn't have otherwise been able to. I really envied him :)