As Mike Darwin pointed out above, we can't reliably tell if a joke comment is a joke.
But you know, this isn't my strongest objection. It's the noise-to-signal ratio. What I'm really concerned about is the opportunity cost of recognizing a joke as a joke, and having to work harder to find the serious branches of discussion.
How much effort did it actually take you to recognize that the comment "GRYFFINDOR!" by a user named "SortingHat" is a joke? It is silly to be worried about the opportunity cost here.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: