I was going to answer in a similar vein, although I don't normally participate in the discussions, mainly because English is not my native tongue and although I think I can now read at the level of a native speaker, I find it significantly more difficult to write in it (and, being a language that for reasons that elude me I love, I hate how artificial and unnatural my phrases sound like).

In my case, I have a background in statistics and biotechnology and I use Hacker News (via RSS) to learn about new developments in machine learning and related technology. I tend to ignore all news related to politics/social issues because HN, on average, has a very narrow-minded (too engineer-like, often ignoring a lot of vital nuances) way of looking at those topics. Also, I'm from Europe and I find that there's a particularly American way of looking at business and personal projects that we don't have here and that I feel beneficial to get exposed to (even with its downsides).

Edit: To expand a little more on my process of using HN, in case anyone finds it interesting, I subscribe to the frontpage RSS feed, so that I usually get between 75-100 stories (just the headlines) per day, which I then proceed to quickly scan to open the interesting ones (both the original URL and its accompanying HN discussion). I've found the signal/noise ratio to be more than worth it (also factoring in the time it takes me to do all of this).