Being more interested in voting as community feedback and less interested in getting the karmic high score, I've taken to removing the auto-upvote on any of my own comments that I would not have upvoted had someone else posted them, then continued to monitor the vote scores for the next few days. I've come to a couple conclusions:

• Most people seem to be voting based on what they think the final score should be, not their personal approval independent of existing score. Most posts ended up at 1 or 2, independent of the default self-upvote.
• Given roughly similar information density, people are more likely to upvote short comments.
• People are far too likely to upvote bad jokes. For a while I think my highest-scored comment was an "Eliezer Yudkowsky Fact". Oy vey.