A couple years ago we decided to use MediaWiki for a wiki implementation at work. Wikipedia uses MediaWiki for their wiki application so we felt it was the right choice for our needs. One concern my team had was that MediaWiki didn't come with a rich text editor (no WYSIWYG).
While a number of us may be fine with using wikitext or HTML to edit our wiki pages, I believe the majority in any organization prefers to edit their pages with a friendly user interface similar to that found on their word processor. At the time, we tried a number of solutions but found neither the suggested TinyMCE or FCKeditor implementation integrated that well with mediaWiki. So for our project we settled with wikEd, an editor that still required users to work with wiki syntax but surprising a very good tool for most users.
During a lunch conversation last week with Deane Barker of Gadgetopia and Blend Interactive, I mentioned my frustrations with MediaWiki not having available a good WYSIWYG solution. Deane suggested that I look at a more recent implementation of MediaWiki plus FCKeditor. This project is being supported by the developers of FCKeditor themselves.