About 8 years ago when I was a parts advisor we had a 4 day work week for a little over a summer. It was great. We were open 7-7 M-F and 7-4 on Sat. As parts advisors our schedule over 4 weeks was MTWT, MTWT, WTFS, WTFS. It gave us, 1 - 1 day weekend, 2 - 3 day weekends, and 1 - 5 day weekend. I didn't have to use any vacation that summer!
Now as for if it was cost effective, I do not know the details as I was only an advisor. But it did only last 1 summer so it must not have been!
Edit below.
BTW, our techs were not on the same schedule and did not like it. As I now recall, I think the techs were the main reason we gave it up.
[This message has been edited by sz (edited 04-25-2007).]