It wouldn't work on me, for example, because I hardly ever vote on anything here. In the 3 years I've been around I can't imagine I've actually voted down more than a half dozen times.
And of course, if downmod meant more "hide this sort of thing from me" than "I don't think this should be on HN", maybe you'd downmod more...
(But this starts showing the downside to such personalization - it's a lot more effort server-side, and it dilutes a single community)
You lost me there. You're talking about this on a site that doesn't even allow its users to downvote stories. And you're talking to a power user of that site, who just told you he doesn't ever downvote things. HN is a culture of voting up things that are good, and, rarely, downvoting things that are distracting from the conversation. That's one of the reasons it's so good.
As to cookies for non-logged in users, they don't really help anything. Sure, you could consider every clickthru as a 'vote' for personalization purposes, but it would likely just fill a user's feed with poorly titled things and clickbait. Probably more than half the articles I click through on get closed immediately without reading. I wouldn't want to optimize my view to include more of that.
The long term cookie isn't really that important for vote counting perspectives but to be able to find out whom to serve the personalized stuff to. It is essentially no different from hn which also sets a cookie when you login, except that if you erase the cookie, you can get it set again when you log in, which wouldn't happen in my example.
As an aside, what makes you a "power user"?