How about a limit on the number of links you can post per day ?
tokenadult: Already in the guidelineshttp://ycombinator.com/newsguidelines.htmlis "Please don't submit so many links at once that the new page is dominated by your submissions."I think reader ennui resulting in a more rapid response of ignoring submissions (or downvoting comments) is the best control on this, rather than any automated solution. In other words, I think current community standards of behavior are working well enough on this issue. Automated deduction of karma may not do much to stop spammers, but readers actively flagging spam posts helps, because a sufficient number of flags autokills a post.