First the author makes the argument that we would drive less. For some reason this is split into eight different reasons that basically just cover the sam negative aspects of driving. And yet, when I think of the absolute worst traffic and congestion of the year, I think of the first day of three-day weekends. Furthermore, the less commuters there are, the less incentive and money there is to fund the infrastructure of public transportation which is one of the only real solutions to traffic and its associated problems (money, pollution, congestion, time spent in traffic, etc.).
He then naively postulates that people would suddenly work harder and skip work less during a four-day week even though their would be absolutely no incentives in place to encourage such good behavior! The idea that people would suddenly start spending all free time cooking, gardening, playing with children and shopping at Whole Foods if they only had one more day off is ludicrous.
My favorite parts though are where he argues how much money we would save! There would be less road work (ignore the fact that a lower GDP would lead to less tax money for roads), less money spent on daycare (ignore the fact that the parent is not working that day at job which undoubtedly would pay more than the money a daycare costs per day) and of course less money spent on consumer goods at Walmart (since if only I had Fridays off, I would never have bought a toaster and plates to eat on from Walmart this month).
Furthermore, what about all of the people who work for the betterment of mankind? The nonprofit workers, the scientists working on renewable energy, the doctors and nurses caring for sick people, etc.?
I am not quite clear whether the author thinks all people with days off spend them sitting on their hands at home spending no money or if he imagines that employers will pay their employees the same for a four-day week as they would for a five. The bottom line is that anyone who thinks a drastic reduction in number of market transactions would increase market efficiency needs to go read some Adam Smith. I will agree with his final point: an extra day off feels great!