I am using Plone as a CMS for the main OpenVZ web site, openvz.org. Recently I also started to use Mediawiki, at wiki.openvz.org. So I can now compare the two engines.

Mediawiki is more of a Wiki than a proper CMS. It lacks some CMS features like article status (private, visible, published, review needed etc.) and (related to the first one) an ability to publish something by the specified time (which in my case is needed for example for press releases which are scheduled by time). Still, for the wiki it is pretty pretty good. I had some experience with TWiki and MoinMoin before and I should say Mediawiki is one of the best wikis available. And since it is used on high-profile sites like Wikipedia, it is proven to be working and it is actively maintained and developed.

Mediawiki is written in PHP and is using MySQL, it's pretty straightforward. I mean, if you want to tweak/change something, it is quite easy.

Plone is just a Zope application (well, strictly speaking, Plone is Zope and Plone is written in Python (which I like). Zope is a tremendous all-in-one piece of software, which incorporates a web server, an interpreters for a few template languages (DTML, TAL, METAL), own object database, full text search engine, users/groups/privileges system and a myriad of other things, most of those are overly complex. Plone adds a layers on top of that, trying to simplify some things. There are some other plugins and components needed, and the whole system is just huge. So it is slow (it takes openvz.org's zope about 30 seconds to start on a dual 3.0 GHz Xeon server), hard to dive in, and terrible.

Zope/Plone will probably work fine for you if you are Zope expert. I am not, and I do not want to be (although now I can do something with it, as I have to). So I should say that Plone is working for me (more or less), but at the end of the day I do not really like it. It is cumbersome, complex and slow (and you can see that it is slow by browsing through openvz.org — although I invested some fair time to make it faster).

OK, those are all ramblings. Let's just compare Plone and Mediawiki from the Joe user point of view. Joe wants to add and edit contents.

With Plone, he have a nice web-based editor, an ability to use "structured text" (or HTML, but not both), and a way to set various states for the document. What he don't have is: (1) document preview function; (2) document history and ability to see changes he just made (although different versions of a document are stored somewhere deep in Zope, and Joe can use 'undo' function).

With Mediawiki, he also have a nice web-based editor, an ability to use wiki markup (similar to Zope's "structured text" but IMO better) as well as some HTML. There is a history of changes available, with the changelog, and Joe can see the visual diffs. Way better than Plone.

Finally, I have to say that Plone is good, and brought in a handful of goodies. For example, those tabs on the top of a document, and a CSS stylesheet for printing. And I am happy to see those features have made their way right to Mediawiki — in fact, Mediawiki developers was quite influenced by Plone, and Mediawiki CSS stylesheets are based on Plone's ones.

To conclude: I like Mediawiki more and more each day. Speaking of Plone, I would be happy to see "Plone without Zope", although it's a nonsense. In fact, Plone is also actively developed (as well as Zope), and who knows what it will look like when it will reach version, say, 3.5.