I did a year of a 4 day/9 hour schedule (our normal work week is 35 hours). I would do Monday-Thursday one week, followed by a Tuesday-Friday, to make alternate weekends 4 days long. For the last year, due to a head injury, I've worked 5 hours a day, 5 days a week, in 2.5 hour chunks. While my hours are shorter, I've found it really refreshing to have a 3 hour midday break. Lunch is never rushed, I have time to watch a tv show or run an errand or two, and I generally come back to work in the afternoon very refreshed. On top of that, it's easier to focus in - 2.5 hour blocks don't leave time for distractedness.

I liked the 4/10 schedule, but I don't think it fulfilled my hopes for it. My intention was to use my off days for my own projects, as I was starting to burn out and feel uninspired. What I found was that it was difficult to shift gears for just a day or two, especially after working long hours the previous several days. For the most part, the off days would just be when I would run errands. Instead of taking a half day to take the dogs to the vet, I would use my free day. So, it was nice enough, but hard to fully utilize well.

Of course, I think the real trick is finding a job that lets you have a good work life balance. My work year, if I were full time, is only ~1500 hours. That, more than anything, is what I'll be looking for in any future jobs.