Ive been working four 4-6 hour days a week for the past year. I’m in my opinion quite productive. I think we need to stop thinking in terms of 8 hour days. An 8 hour work day is a lot! Same with five day work weeks. With four day work weeks you get perpetual three day weekend and that makes a huge difference. Actually recently I started working Monday and taking Tuesday off so I can attend a Tuesday night hack night at the local hacker space that I would not be able to attend on a work day.