We allow each staff member to set their own commitment to the firm. We now have several staff members with no desire to move up...they just want to do the work and go home to their family. Some of them are part-time; some work a forty hour week year round; and some of them are full-time plus.
The firm members that had the hardest time dealing with it were the nonpartners who did want to climb the "ladder". They got jealous when their peers were leaving at 5pm and they had to stay late. We eventually lost some of those people, which ended up being a good thing.
The firm members that we hired to replace them knew the firm culture from day one. They understand that everyone gets paid based on the hours that they work. They also understand that their efforts to move up the ladder will be rewarded in the future.
We don't all have the same priorities in life. Some people want to climb to the top in their profession and some people just want a place to work. We have made a home for both at our firm.