I work a four day workweek and have been for a full year now. I'm likely to never return to a 40hr workweek. I actually ended up interviewing at a few places a couple of months ago (Capital One, Farmers, few other smaller companies). I was pleasantly surprised by how many hiring managers and HR folks were willing to talk to me after I mentioned that I was only interested in 32hrs/wk @ 80% salary. My point of advice to anyone who is curious about a four day work week is just do it. Ask and I'm willing to bet you will receive.
Do you still get fulltime employment benefits? That seems to be the sticking point with many companies, as fulltime and parttime employees are treated, and cost, different, even if salary is prorated.
That's wild to me because it's my understanding that most HR departments consider anything over 30hrs a week to be full-time. I didn't encounter any of that last time around. My offer from Farmer's included a pension and full benefits. I'm a small sample size though...
