One of the most interesting things about this site is the karma scoring, and that it reflects (to a greater degree than you see elsewhere) an objective assessment of the merits of an argument.
[Edit^6: the proposal in this post is related to the Kibitzer system, but this post discusses adding information, while that system concentrates on taking information away. Special thanks for matt's comment and to Vincentyu for being the first to point to prior discussion. A related issue is discussed here (2009) with reference to a wikipedia, and on which Eliezer said "I may end up linking this from the About page when it comes time to explain suggested voting policies"). Data: It took me ~2 days of effort to obtain get linked to this information (09 June 2012 11:29PM -> 11 June 2012 10:28:26PM).]
Suppose a controversial post/comment has six up votes and three down votes. Right now we only see the net result: 3 points, but when the voting is mixed we're losing important information. If it's reasonably easy to implement, could we please show up and down tallies separately? E.g show "3 points (+6,-3)", at least when the voting is mixed? I think the negative votes are the single most important thing. In particular, I want to know about negative votes I receive and where I receive them, because those are the posts where I need to think carefully.
Example: here's a welcome post by syzygy, which relates to Eliezer's post about Politics as the Mind Killer. I know that it's controversial, because I can sort by controversial and it shows up high on the welcome post thread (neat feature!), but I can't tell how many down votes it has. Does syzygy commit a fallacy? (I don't mean to pick on you, sorry about that; I liked your post.)
Of course this change wouldn't fix everything. If a post has "-1 points (+0,-1)", that doesn't mean only one person read it and disapproved; maybe 100s read it and thought it was bad, but saw that it already had -1 net and considered that sufficiently punitive. This is pretty good; we don't want to spend all our time fiddling with scores.
I mean if we wanted to get fancy and use Bayesian inspired scoring, we could let everyone who wishes assign a score (say from -5 to 5) and report posterior summaries of the scores. Or, more importantly if we value objective scoring, we could identify posts that are controversial and we could have the system randomly select users with respectable karma, and assign them to give their score on the post. Such a score would be valid in a way that the current "convenience" scores are not. Additionally, posts could be scored on multiple axes: soundness of argument, potential impact, innovation, whether we agree with the normative basis of a judgement, etc....
But I'm not arguing for a complicated change, just a simple less wrong one.
Other than feasibility concerns, or maybe aesthetics, the strongest argument I can see against this proposal is that we might embarrass or shame users. Can any one give an example where that might be a concern? I figure that since we already show negative scores, users have gotten over most of that inhibition, but I'm new here.
Another possible criticism is that it's a non-issue: almost all posts are all plus or all minus, so it's not worth the effort. I disagree with this one because I think the posts where we have mixed judgements are the most important ones to get right.
EDIT: Wouldn't it be nice to know how many down votes this post has?