Currently, the comment for which I've received the most positive karma by a factor of four is a joke about institutionalized ass-rape. A secondhand joke, effectively a quote with no source cited. Furthermore, the comment had, at best, tangential relevance to the subject of discussion. If anyone were to provide a detailed explanation of why they voted as they did, I predict that I would be appreciative.
Based on this evidence, which priors need to be adjusted? Discuss.
I haven't upvoted the joke, mainly because I think that jokes generate more karma than I think they are worthy, and thus I never upvote jokes since the moment I made that observation. But hadn't I the deliberate policy of never upvoting jokes, I would simply upvote it because it was funny.
Remember, upvoting here, from a single user perspective, is a boolean scale. A good comment earns my single upvote, a bad comment earns single downvote, while most comment pass along without my voting because a) I don't read them for different reasons or b) I am not sure whether they are good or bad.
If you make a thoughtful comment, many readers aren't interested to read it and skip it, because it is probably too long, or because it is incomprehensible, or because they aren't interested. From those who read, they would need to think about it for a while before they realise that the reply was really good, and maybe forget to upvote afterwards. On the other hand, a joke generates quite a few instinctive upvotes at the beginning, which makes it even more visible (I tend to read upvoted comments first and more carefully), the visibility then generates more karma.
Nobody is responsible for the others' choices and thus for the fact that the comment stands now at +16. For any single user, the joke is at +1 as well as other better posts, which (s)he is aware of. We want to hear good jokes and thus want to reward them somehow, and the system doesn't allow to differentiate between them and the information-bearing intelligent comments. I suppose that if it was possible to upvote on some more continuous scale, the seeming discrepancy between the individual preferences and the collective voting results would disappear.
Note, for comparison purposes, that this related comment stands at +10 after 22 hours.
Edit: The parent stands at +4 after 24 hours.