This phenomena can be seen in forums without karma also but i think in places with karma it is usually worse, worst offenders being digg and reddit where everybody tries to make a silly joke as those are easy points.
A better algotithm calculating the karma as an average over all your comments maybe could help..
It's validating to get a few upvotes, but more than that it's disheartening to spend time on a comment and recieve no feedback whatsoever.
I'm an outgoing person, but I find myself shying away from commenting on HN for that reason. Admittedly, I don't usually have some brilliant insight, but it does make it harder to feel like part of the community.
The metric I would most like to know is how many votes my comments got divided by the total number of words in my comments.
On the contrary I often learn useful things from HN comments. Sometimes I even submit stuff to HN because I am curious about the opinion of HN commentators.
b) there are downvote arrows
To me it's OK if people just leave anything as a comment here because it will be modded down if it's irrelevant to the discussion.
My reading buffer most certainly can.
If the s/n dips sufficiently, I'm out.
It's the Yogi Berra Restaurant Syndrome, or the Evaporative Cooling Effect:
http://blog.bumblebeelabs.com/social-software-sundays-2-the-...
It would be great if down voting was more prevalent. Many people don't down vote for anything but the absolute worst comment. Some people downvote for disagreement and not poor comment.