It would be hard for me if I ever have to go back to 2 day weekends. I think psychologically what makes the biggest difference is finishing the second working day of the week. After finishing the second working day, in my mind I know that I'm halfway done with the week. But with 5 day work weeks, after finishing the second working day, I still have 3 more working days. I know it sounds like something minor, but psychologically it makes a world of difference to me.
I hope 3 day weekends becomes the norm