I have been working on content management for more than a decade, and i wrote my first content management system in 2002 (used by my current employer and also by some websites (playscope.com, aysun.org, loveticket.com, parismontmartre.org, ...). Features like tags, classification, related documents, search engine, themes, rich editor, taxonomy, collaborative filtering, peronalization, users management, communities, rich media, marketing rules, content ordering are currently available on it.
But the question i'm asking myself now is : is it worth doing to redesign a content management system nowadays ? I like to code, but i have to rebuild all from scratch now, and to introduce web services on it, i have all the ideas on how and what to do, but it's quite difficult to build this alone and after work. Well, I should do it and firstly work on the webservices (and new technologies of course : openId, rpc, wcag-aa, gwt .. ), i hope 2008 will be my rebirth on the Internet (more post to come with samples screens from my cms soon).