While the two variables may be orthogonal for an individual, in aggregate they tend to be the same thing.

To illustrate starting with the most stark case- try to imagine a comment that 0% of HN readers agree with but that 100% feel is a valuable contribution. I can't, and the reason I can't is because usually when I encounter the "valuable but disagree" situation individually, it's actually me thinking "some % of other HN readers may share this misconception, therefore it makes more sense to respond than to downvote." or "I disagree with this, but I know most HN readers won't." Or, rarely, "I disagree vehemently, and feel obligated to make that disagreement known because the 5% of readers who actually agree really need to know why it's [dangerous/silly/misguided...]"

If the poster is the only one in HN-space that agrees, no matter how "thoughtful" (i.e., verbose, in that case; possibly like the comment I'm writing now) it is, it's not important. The fact that some percentage of readers agree* or may agree is what gives it importance. In aggregate I'd suggest that the number and ratio of upvotes to downvotes would match the importance as defined by the community.

In this context I'm using the word "agree" in a sense a little broader than usual. Instead of "I take that position to be my own"- an upvote is broadened to "I can see myself taking that position as my own after further reading/thought/experiment," and finally even "This line of thinking is attractive to the kind of people I like to have in this community."

Where things get muddy is when we take that even further and say to ourselves "Some percentage of people will take that position even though I will not. Therefore it is 'important' and I will upvote it." Kudos to the altruism and social empathy, but imagine if 100% of HN readers thought this way. A position that is shared by only 5% of the community would have the same number of votes as a position shared by 90% of the community, even pithy one liners and mean-spirited ad-homimems. In a more likely equilibrium, a percentage of people will do an "importance" upvote for an item separate from their agreement with a probability roughly equal to the number of people who actually agree with the comment (So, there's a 1 in 100 chance that I'll give an "importance" upvote on an item that roughly 1 in 100 people would agree with). That would keep the proportions more or less sane and only result in general karma inflation.

Whew, hopefully showed my point- aggregate agreement _is_ relative importance- even if the individuals agreeing and upvoting are not the same people. I could go on with a parallel line of thought for disagreement, although with slightly different results (it's probably a lot less likely that one thinks "While agree with this, it's not important." or "I agree with this and it is important, but x number of people probably don't agree with it so I'd better give it a downvote to be fair...") In fact maybe, the difference between the two sides is key to the bigger questions of site quality degradation.

So, to the bigger question: possible reasons for degradation that I've thought about and seen discussed so far-

* People trying to decouple agreement from importance and therefore end up trying to channel the thoughts of others, leading to inflation and biases in all sorts of weird ways due to a social instinct that is, by itself, very positive and healthy.

* The blind leading the blind (avalanching) that pg is experimenting with solutions to now.

* Scariest of all because the fixes are more difficult: The community, in aggregate, is not as valuable/smart/insightful as it was. This compounds the problem with the first point- What happens when some percentage of people (say, greater than 10%) genuinely find "You're a dirtbag" insightful? It trumps the other two points even if they're perfectly solved. What happens when 80% of readers thoughtfully proving comments turns into 30% of readers, with the other 70% just there to "learn" and follow the lead of the 30%?

The last point is the most difficult to solve, but there are several methods- there are tweaks such as the "only posts from old members" hack pg did, the green names for greenies, etc. Then there are more frontal attacks: Doing everything you can to lift the collective thoughtfulness and intelligence, and discouraging, sometimes via use of the downvote, comments that aren't worthy of the community.

With all three happening at once, the system becomes very difficult to understand. Some suggestions:

* Let your vote reflect your degree of agreement/disagreement, AFTER giving it some serious thought. Feel free to not vote either way and to post follow-up thoughts or questions instead first.

* Refrain from voting as an emotional reaction or indiscriminately to simply feel more a part of the community.

* Try not to take downvotes or upvotes personally.

* Never pass up an opportunity to try to crystallize your own thoughts and lift the collective intelligence of the entire community by responding with care, whether expounding or disagreeing.

* Never pass up an opportunity to downvote comments that genuinely degrade the intelligence of the discussion ("frist p0st", personal attacks, almost anything that is a single line and contains no wit...)

* (more I'm sure but this post is getting way too long)

EDIT: formatting