Another possibility: when submitting a link, simply have an automated check against previously submitted links, and give an automatic upvotes or two to the prev

Another possibility: when submitting a link, simply have an automated check against previously submitted links, and give an automatic upvotes or two to the previously linked submission. In this way, if a bunch of people resubmit something (say, an old article is making the rounds on the net yet again), it will have a chance to be brought back to the front page - with all the previous discussion - so that HN can stay a place where people can discuss the hot topics of the day, even if the "hot topics" happen to be four years old. This aims to solve the "double discussion" problem, but it won't fix the "I don't want to see it again" problem.