It seems that if you look at the column on the right of the page, you can see upvotes and downvotes separately for recent posts. The same [n, m] format is displayed for recent comments, but it doesn't seem to actually sync with the score displaying on the comment. This feature only seems available on the sidebar: looking at the actual comment or post doesn't give you this information.
Thanks, whoever did this!
This is actually a bug, not a feature. Some major changes to how karma is stored and passed around the application were made in order to implement the percentage tooltips. Scores are now passed around as an array containing the number of up votes and down votes, where previously it was the difference of the two. It appears the this array is being incorrectly rendered in the side bar, instead of the calculated score.
I think this is bug is actually an unintended feature.