Looks like we'll finally be ditching MediaWiki in our office next year. Apple has come to the party with a WYSIWYG wiki of its own: http://www.apple.com/server/macosx/leopard/wikiserver.html
We've been using MediaWiki for our office intranet over the years but it's never been adopted to a level that we think it could be, because of the requirement that users learn wiki markup.
It's always surprised me that WYSIWYG editing has not been a high priority for MediaWiki, considering the fact that MediaWiki and Wikipedia are founded on the idea of participation. The biggest obstacle, it has often seemed to me, is an installed base of Wikipedians who see wiki markup as a way of protecting their territory and minimising participation by others. MediaWiki has therefore been a bit of a love hate relationship in our office, and instead of being sad to see MediaWiki go we will be very happy indeed.
Thanks to those who have been working on WYSIWYG for MediaWiki, particularly in trying to integrate FCKEditor. I wish your efforts had borne fruit earlier and it's a pity you haven't had more support, but I'm sure you'll get there eventually.
Cheers, Christiaan