To be very clear so as to prevent conspiracy theories, this is something that we never did on reddit because we didn't want to put that much power into the hands of the older users. However, HN has a different philosophy and it might make sense here.
To say it one more time, reddit doesn't do this and never did.
Google is the best example to learn from. Search is a misnomer, Google is about ranking. They've put many PhD-centuries of effort into deciding which of the three million matches to put first (ranking). Choosing the three million matches (search) isn't where Google adds its value.
Lots of lessons have been learned there, I'm sure HN can tap into that pool of knowledge by opening up data to the right people.
HN is an awesome resource. I often read the comments before the articles because I expect them to be more useful.
It's completely worthwhile to invest a lot of effort in maintaining that greatness as it scales.
Sorry I couldn't help myself.
EDIT: (total rewrite)
The cool thing about using metrics and machine learning is that the results speak for themselves and opinions and factions are less important. Intead of guessing what matters in advance, you get to discover what matters after the fact.
On the other hand, either of these solutions seems destined to increase the inevitable echo-chamber herd mentality groupthink that already tries to creep into any community.
I often find the news here, so I'm very unlikely to submit something. And I only comment when I feel like I'm going to add value to the community or discussion, which isn't that frequently. So I have a clear judgement on when I contribute, it's not much or often, but it tends to present some value.
I've had an account for 2.5 years, and used the service for even longer, yet my karma is still less than 300.
I do frequently vote up good articles regarding programming, hacking, startups, and such things. That's the things I'm interested in since I was a young boy and that's my daily life. I'm a freelancing coder (yes, I see that term as positive, same way as hacking) since '96 and tried my own startups since then over and over. That said, I value good and constructive and sometimes also funny comments and being able to upvote them I frequently do so.
Are my upvotes even counted? I don't know, I don't really care. But I admit it gives a bit of a strange feeling to be "less worth" in a community where you participate - we can argue about that - daily.
Nevermind, just wanted to say.
Small addendum: After submitting this comment I remembered that I wanted to add that I'm from Europe and people not being from the States and therefore in a different timezone often experience to comment on already discussed topics (this also happens on Reddit a lot). Maybe this is also a part of why I'm not commenting that much.
I see the necessity of moderating however there has to be other considerations. i.e a number of lower karma users can override the high karma users decisions.
Of course, this forum isn't a public commons so the moderators can ban whoever they want, but there are some cases where it seems fairly arbitrary.
(By the way I would summarize why I disagree now that I've written the above as simply that it seems like a "last man over the bridge" advantage. I mean it's entirely possible that some distinguished person whose vote should count would be greatly disadvantaged by the weighting system you propose.)
I hate to complicate things but there doesn't appear to be anyway to solve this issue w/o the ability to indicate more clearly what you feel is positive or negative about a comments. One up/down button simply can't cover everything.
Also, you can't count on there being proportional amounts of activity among the earlier users currently. Any cross section of the earlier user group could have stopped being active on the site.