You could even have everyone's HN be seeded by his own upvotes/downvotes. Everyone would then get their own HN with stuff they like on top and stuff they don't like on the bottom. A tagging system would also help a lot. People who are interested in politics get politics, people who are interested in science get science. I'm not sure if these are good ideas however, because you might get multiple ghettos (and it would be hard to implement).