I am currently doing a (simple) sentiment analysis for the complete reddit comment set. Perhaps when I am done with that, I can have a look at the HN corpus (where to download?) for correlations between upvotes and users, though I doubt that rating post quality by sentiment is easy.

But it could be useful to look at the comment history of a user. When someone who is an overall positively minded contributor (with a high average positive sentiment) suddenly writes one scathing reply, this could mark a potentially interesting thread.