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.
There are other effects as well, status of the commenter included. People are more likely to read longer comments if the author is known to make good comments. I guess that this effect is weaker for shorter comments where the evaluation of actual content is easier. So, low status karma maximisers should write a lot of brief comments, and as they reach high status, they should swap to longer "walls of text".