- The post is factually right / wrong - Confirms to the site rules / breaks the rules - I agree / disagree - I want to promote / bury this post - Reward poster with XP / punish
I am usually very pragmatic and upvote a post when I want other people to read it (because I want to see the discussion, or because I want to spread the idea). I also upvote to reward the poster.
I don't tend to downvote factually wrong posts when they are still interesting, because that limits the chance they get good discussion, and because I don't want to punish somebody for Being Wrong On The Internet. I do downvote positions that I find bad in order to reduce their reach.
It would be probably possible to have a site that implements two dimensions as a cross (maybe only for users with a certain XP) although the UX might not be to great. Maybe it is a good idea to have "promote/bury" and "reward" buttons?