Immeasurable. I don't do any social media, or networking. HN lets me know what's hot, and I can filter whether or not I need it myself. HN brought me Golang, and I wouldn't have found it so early otherwise.
My first thought was hn has negative roi for me as it is a time sink. But, like you, I first learned about Go here. A couple of folks at work and I introduced it to our org some maybe seven years ago. The org became a Go shop. I vastly prefer coding in Go compared to AnyEvent Perl or Twisted Python. So, hn has had a very big impact on me; immeasurable.