Idea for the merge mechanism. If a user thinks a link has been submitted before; the user posts a cross reference comment whose syntax must be simple as in: MERGE: news.ycombinator.com/link/to/article

If the merge comment gets enough upvote, then a detection algorithm automatically merges it to the other one.

I left out a couple of details, but this is the simplest way I can think of to automate the merging without reverting to clustering algorithms.

I guess this is equivalent to voting the story down the front page, but it allows for salvaging the discussion in the down voted link.