Not an admin, so I can't speak to what they have available. But as a hacker...<p>Since the usernames are not queryable via an integer (e.g. user?id=1235654321) it's not exactly the most trivial of things. You'd have to go through an endless amount of posts, get every possible username from the comments, go through all stories submitted, grab their usernames, and then loop through the HN API and grab karma info.
I just noticed my profile had a section explaining average karma. But I don't see where my average karma is shown. (Or is my main karma number actually the average it's talking about?)