Ironically, solipsist, the user who posted this, has an account less than a month old with 2120 karma. Based on my casual observation of the new stories page over the last month this user submits a lot of stuff. There's not necessarily anything wrong with that. But submitting a lot of stories is a good way to get lots of karma quickly, since stories are voted up more highly and it takes almost no time to do.
I agree that the downvote karma threshold has been instrumental in maintaining the quality of discussion here on HN, but it seems like it's too easy to get around by submitting lots of stories. And that drastically reduces the socialization period.
You're definitely right, solipsist has submitted 26 articles so far today!
The obvious solution is to limit the number of articles you can submit a day to, say, 1. Increase the scarcity of the resource to increase value of what it's used for and limit the power of karma farmers and spammers.
Seems as if it isn't that hard to bypass the "trial" period of HN. In addition to minimum karma requirement, applying 3 months of newbie time would probably be somewhat helpful as well. If the user has earned his badge of negative voting after the end of the rookie period, his understanding on the site has matured to point where he knows where the site is at, and he would be more than willing to keep it that way.
Another option is to have story submissions not count towards karma. Presumably one should submit a story because they think the community will benefit and they want to share it. If you give people cookies every time they submit something, you'll end up with people who only want the cookies.
I agree that the downvote karma threshold has been instrumental in maintaining the quality of discussion here on HN, but it seems like it's too easy to get around by submitting lots of stories. And that drastically reduces the socialization period.