Recently I've seen two trends, both of which significantly diminish the value of Hacker News:
1. Some users are flooding Hacker News with submissions (in one case I counted 18 submissions in one day), and even though most of their submissions aren't being voted up, enough submissions are to make them accumulate lots of karma (which I assume is why this is happening).
2. The same stories are being posted many times by different users. I'm sure this is partly the result of #1 -- with the floods of submissions users might not realize that a story was submitted before -- but the fact that there's no "penalty" for useless submissions probably contributes as well.
Re #2, I always thought there was a unique url filter on submissions, but I've seen a couple repeats recently.
Even with different URLs, there's really no need for 10 different stories about the MacBook Air to be posted here -- it would be much better to have one Hacker News item and have URLs to other articles posted in comments.