James Robertson just posted another great article on usability called 11 usability principles for CMS products. I think all of these principles are worth keeping mind when selecting or building a CMS (or any software for that manner). In response, Adriaan Bloem of Radagio posted this great comment on the CM Professionals mailing list:
Much of what makes web 2.0 examples work is based on the fact that in one way or another their use is much more intuitive than that of "classic" content management systems. Everyone can relate to the fact that a blog places the newest item on top; or that a wiki links through keywords; or that you can simply enter a couple of tags on a photo site and you'll be able to search those. "They make it look so simple", yet what we see in CMS interfaces is another turret, flag or tower on the castle and a little bit of AJAX thrown in to be buzzword-compliant.
I can't even count how many CMS products have added drag and drop sorting to their old "operating system" of a user interface just to claim they understand and deliver a Web 2.0 experience.