My average at this moment is 7.64. By giving all this weight to avg. karma, the message from the site to the users is clear: "higher avg. karma is better, work to improve yours". In my case, this means I should make a comment only if I expect it to get 8 upvotes or more. This in turn means that I should not respond to replies to my comments, as they rarely get to 8+. I should also not reply to articles late in the game as it's unlikely to get to the threshold also. So what will I respond to? Early threads where I feel I can make a contribution. It is also unlikely that I will make 'eccentric' comments that are a risk in terms of votes, but may help break the echo chamber as this behaviour is not encouraged. The only other case I may make a comment is when I feel strongly enough about something that I am willing to take the hit, as in the case of this comment.
Now, many will say that I should ignore karma altogether and that I should just participate in the community as if it didn't exist. For one thing, this is orthogonal to the discussion here. pg has made this change to alter the community's behaviour, therefore he expects it to have an impact. Even if I chose to disregard it, nothing will change in the general case. Secondly, poster avg. karma affects ordering of comments and therefore the impact that your comments have. So it materially affects your experience in this community, and when I have something to say that I feel needs to be said, I benefit from it having the highest possible impact. This makes me care about avg. karma in all other situations.
On the other hand, submitting articles is not subject to such pressures, so I will happily continue doing that.