The CMS should be simple and while researching I discovered the shop talk show (Episode 240: Rapidfire 76).They discuss some verty important points throughout their hour long discussion.
Firstly, people working at the company change, both the developers and the clients. It is important that both parties have the ability to add and remove users from it’s cms.
Also, most clients will have no technological ability whatsoever, therefore it is important that the users have the most simplistic interface possible. A great way to do this would to have a live edit mode that allows the user to browse the site and change content just by clicking on it.