[badbug]

This assumes the user is accurate in his interpretation of a comment.

Once they learn that "a" makes comments more visible and "b" makes them less, it just becomes an agree / disagree vote

[beaconstudios]

I'm not suggesting an upvote-downvote system though, but a per-user "flag" that can highlight 1 article per day. No downvote option, and the UI would highlight its intended use.

[badbug]

The upvote is an implicit down vote for other things.

I think you need two things. First an upvote/downvote so that users can express their agree/disagree. This value wouldn't necessarily effect the visibility of the content. Second, a sort of budget system where users can trade earned karma to classify an items "quality".

I think this would lead to a system where you would spend your karma on the communities you care/know/like the most. If I were, for example, a blind apple hater, the upvote/dowmvote makes it easy to downvote apple content or upvotecother content to push it down the page. But I may be more inclined to save my karma for promting Android content instead.