we've got a 35 hour work week that can be split 4 or 5 (or 4.5 if you'd like to come in every other Friday...)
a 4 day workweek is like crack - I've got an extra weekend day to get things done at my own pace. go shopping when no-one else is in the malls, work on side projects, spend time with family - whatever...
Retention here is waaaayyyyy higher than any other tech job I've worked. It's easier to put up with the office politics and bureaucracy when you've got an extra day off.
BTW - Mondays off is better than Fridays off. All the problems and meetings happen on Mondays while Fridays are normally more laid back and leave you with time to do work instead of slogging though status meetings and production issues that occurred over the weekend.