With the success (in terms of points, badges etc.) of questions like Is this rotating cube interface user-friendly?, does the system encourage questions with (arguably) low UX value, but which are contentious or funny?
I would say we're on similar ground as Amazon's Three Wolf Moon Shirt and many fun questions on Stack Overflow. The question/comment was obviously facetious and thus serves only to amuse rather than confuse , see Jeff Atwood's post on "Joke Questions" vs "Fun questions."
Amazon presumably leaves up funny product reviews because it attracts users; people willingly flocking to what's basically advertisement is one of the best things you can get in marketing. At the same time the reviews like on the Three Wolf Moon Shirt are clearly for fun and no one is going to seriously buy the product because of mocking claims made in silly reviews; they may however purchase the shirt as a joke or simply because their attention was drawn to it.
As a Q&A site a more formal atmosphere is important, but I think a little fun can be okay, and I think the most important thing about this particular question is that it promoted legitimately interesting and thought provoking answers. Roger's Answer on the question is a perfect example, while remaining jocular many interesting points were brought up.
Bottom line, it raised awareness of the site and it hasn't spawned "me-too" joke answers best I can tell. I don't think we're encouraging it "joke questions", but I think this particular one has encouraged us.
I think the site actually discourages joking around because people don't come to Stack Exchange to laugh. They come to ask questions and get answers, and although you it doesn't hurt to include humor in your questions/answers, the main focus of what you write should be the topic at hand.
If it was any different, the quality of Stack Exchange sites would start to drop, and there would be little to differentiate us from Reddit, etc.
So I think the system is pretty good as it is now. And the great part about the 'meta' sites is that things are always open for discussion. :)