I'm in somewhat of a unique position to comment on this, since I both do MediaWiki extension development, and run a MediaWiki consulting company (shameless plug: wikiworks.com) - so I personally have a financial interest in making MediaWiki more popular and more easy-to-use. I also tend to hear a lot about the specific frustrations people have with MediaWiki, which has led to my development of certain extensions, like Admin Links, which defines a page meant to serve as a "control panel" for administrators:
http://www.mediawiki.org/wiki/Extension:Admin_Links
Troll-like as the original email was, :) it brought up some fairly common complaints. The basic answer to these is that they are, in fact, being addressed: as a few people noted, the usability initiative has already created a much nicer skin, Vector; and a planned project for the upcoming Google Summer of Code is to provide a way to install and manage extensions via the web browser, the way WordPress does it. A few extensions, like Configure, also allow for a web-based substitute for editing LocalSettings.php, though they could stand some improvement.
Finally, on the more general subject of Wikimedia's relationship to MediaWiki: I do think it would be nice if Wikimedia, and outside MediaWiki developers, were more aware of, and more positive about, MediaWiki's popularity in the outside world. It's used very heavily as an enterprise wiki around the world, and I think for good reason: it's robust, stable, very feature-rich, heavily translated, and when used with the set of extensions around Semantic MediaWiki I think it's in a class of its own. I just think a better answer when people ask about problems with MediaWiki is to say "I don't know", or "I think someone's working on that", rather than "MediaWiki is intended for use by Wikimedia projects, and if you have a problem using it, you should switch to another wiki application." First, for many uses there is no better wiki software, especially not for the cost; and second, there are a lot of people, especially among extension developers but also in general, who are trying to improve MediaWiki as a corporate/organizational application. I just think it would be nice if more people celebrated MediaWiki's popularity, instead of ignoring or trying to discourage it. :)
-Yaron