Once you're a regular, it's hard to change your karma avg that much. OTOH karma points can go up or down one point and that's an instant visual sign people agree/disagree with you. Then you go right to the threads to know where.
It was only the last 50 comments, I believe. But it did update too slowly, as other people are saying.
i.e. I can upvote or downvote someone, but not see the current score their comment has, or their overall karma, or my own.
What happens then? Do we stop our subconscious trepidation over whether we will be downvoted and begin posting whatever pops into our heads, thereby improving HN, or do we begin posting a bunch of crap because karma no longer matters, thereby worsening HN?
it also reduced the value in commenting on old but important threads because they would not be as popular.
I think any simple average is wrong. Would you buy a stock based on it's average selling price over the last year, and compare year to year? Plus in stocks there is risk. I wish karma was more of a market, and had intrinsic value.
The current system of total karma encourages people to avoid comments that will get more downvotes than upvotes. Avoiding more downvotes than upvotes is not exactly the same thing as avoiding comments that won't get upvotes.
I would guess that they found it to be useful information to have about others, but also wanted to eliminate the incentives created when people try to push up their averages. It also becomes a much more accurate indicator when people aren't gaming it. Of course, you could still game it by having a friend tell you what it is, but that's probably more trouble than most people are willing to go to.
but I think it might still have some merit for those with less than 200-500 points, so that they'll try to give better comments