There is no doubt based on page hits and links that Wikipedia has been hugely successful - I've even seen attributed quotes from Wikipedia used on advertising in a staff canteen at large factory!
"The idea behind Citizendium is to improve on the wiki-model by adding what they call "gentle expert oversight" -- which more or less means that qualified users approve articles before they are officially added to the encyclopedia. Further, contributors are required to use their real names...
Citizendium marks files in three ways: CZ Live (articles being written), Approved (articles that have been given the stamp of approval by experts), and a separate draft status for previously approved articles that are being edited."
Considering this is the aim, then anyone interested in social software should be interested in following the success or failure of the Citizendium approach, particularly for Enterprise 2.0 adoption - i.e. can we really tap into the wisdom of the crowds with a self-regulating system or do we still need oversight.
While Read/WriteWeb stress it is a little unfair to compare the two sites at the moment, it is rather telling at the moment that the Wikipedia entry for Citizendium has more to say than Citizendium's own page on itself. Issues of how much content aside, the other issue appears to be the timeliness of new information being added. There is of course an overhead to stronger editorial processes, which ironically inside the firewall is one of the reasons why there is so much interest in using wikis for intranets versus traditional content management approaches.
Incidentally, Ernst & Young's approach to Knowledge Management was based on the idea of "filtered" (i.e. processed, reviewed and managed content) and "unfiltered" (this included discussion forums) knowledgebases. The infamous PowerPack would have been the internal equivalent to Citizendium, while other document libraries might represent Wikipedia - this was all linked together by a search engine. The same issues around the amount of content (deliberately) and speed of information collection existed with PowerPacks. But when a PowerPack was managed well their reduced size and high quality content were valued - so perhaps there is room in the user-generated content stack for both managed and unmanaged content.