In all my work history I have always had a 5 day work week. Either Monday through Friday in the IT field or Tuesday through Saturday in retail. I am working at UserScape now and we started summer hours two weeks ago. Which basically means we get half the day off Friday.
Honestly going in to the first week I was a little worried I wouldn’t get as much accomplished as I wanted. Now that we have passed our second week I think I get more done on Friday than some of the other days. My mind shifts from thinking about what I can get done by the end of the day, to what can I get done in the next 20 mins. Friday mornings feel like a sprint and I am focused on getting as much done as possible. This means I take away as many distractions as I can. (rss, email, im, etc)
Not only do I feel very refreshed coming into Monday and ready to jump in but that extra time with the family is awesome. I don’t know about your weekends but mine are so crammed full of activities it goes by really really quickly.
If you are an employer I would recommend you give something like this a try. You may find your employee moral improves and more things get done in less time.