After being a member here for years I recently got the ability to down vote after making a well timed post. I've only used this power a little bit, and I think only on way off topic comments or jokes. I hope over the years I've up voted a lot more, and mostly on things I found insightful, even when I disagree, because that's the community I want to be a part of. Voting to agree or disagree is not really the best way to foster effective exchange of ideas. I hope that is what HN is still for. I've learned a lot here over the years thanks to the insightful and differing viewpoints one can find here.
I think I've also used this power to down vote completely incorrect information a few times.
But I usually read when not signed in and then I can't vote at all. And honestly, I think it was a pg comment that talking about voting and karma is boring. Either the post is valuable or it's not.