Hi! I've read that usability is important for MediaWiki. Why don't integrate wikitext syntax highlighting then? That will greatly improve editing of the pages. There is Extension:WikEd which has most of the work implemented already. http://www.mediawiki.org/wiki/File:WikEd_screenshot.png I know that it should be possible to install the extension separately. But I remember that important extensions are sometimes integrated into MediaWiki. There's also FCKeditor, but it cannot perform diffs, and visual editing is not always desirable (non-technical users like it, but I personally prefer to edit wikitext).
It just comes to me everytime I edit source PHP with hightlighting, then editing wikitext without highlighting :-( Dmitriy