A lot of dumb comments appear to germinate on threads that are the 3rd or 4th take on some tech news story about Facebook or Apple.
But this?
the duplicate posts which happen a few months later
Once we're up to a timescale of months, or even weeks, we're no longer being sensible. Instead we're exhibiting FAQ Syndrome: The irrational fear that someone, somewhere, is saying something that isn't entirely original.
I think the cult of originality is actually a big problem at HN, and other "news" sites as well. The important things in life are not particularly original, and they do not change particularly quickly. A site that is determined not to re-discuss previous topics is doomed to discuss nothing but ephemeral trivia. The great thing about celebrity gossip is that it is always new! We can manufacture celebrities at whatever rate is needed to keep the front page fresh. But we can't manufacture Knuths as needed; we've only got the one set of Maxwell's equations; new books on the scale of K&R or SICP don't come along every day. But if we discourage the constant reexamination of these classics they will get placed on the dusty shelves and we'll see nothing but discussions of the latest gossip and bling. You know, like we have today.
I always wished HN would feel more like academia, which cycles like the seasons. Every year, you discuss all the classics again for a new audience of newbs. After a little while, you've heard all the classics and are ready to graduate, or become a professor. This is what makes me miss the days when this was "Startup News" and was more explicitly tied to the YC cycle, the time when you could tell that a new YC class was starting by watching for the influx of new people.