Plone is a popular Open Source Web CMS based on the Zope application framework. A recent review of Plone by Roger Johansson is definitely worth a close read if you are considering Plone as a Web CMS.[Editor's Note (4-Oct-2007): Check out our case study on how Discover Magazine uses Plone as a primary publishing platform.] Roger is a Swedish-based web developer sort, with an emphasis on presentation technologies, web standards, and the like. Accordingly, his review is skewed in that direction, with a careful critique of Plone's XHTML output, including some very practical tricks and tips for tidying up those areas where scores were below average.
The server-side of the story is unfortunately not examined in as close of detail. Roger does touch on the challenges associated with breaking the Plone mold and crossing into the land of custom content types and general server-side customization.
To quote the man himself, "Plone is a very powerful and highly extensible CMS. It’s just incredibly hard to learn to develop for, especially if you don’t have any previous knowledge of Zope and Python."
..and from our view, that's the crux of the matter with systems like Plone. If you regularly get your geek on with Python, this is a viable option. If you don't, you'd better think twice before locking yourself into a technology that is not core for you or a significant chunk of your tech team. Read the review and when you're done, check out some of Roger's other articles. He's definitely got a lot to say and does so in a thorough and authoritative manner. Of particular note is his approach to managing nav button states with in CSS. [Thanks to CMSWatch for the pointer.]