As for me, I care about the karma scores of each comment of mine (because they show me whether readers think my comments are insightful, out of whack, or neither in particular), but not about my total karma (so that when I'm asked to pay a toll to reply to a heavily downvoted thread, I hit “Proceed anyway” with no hesitation). Likewise, the score of all of my latest twenty comments decreases by 1 in 10 minutes I realize that someone is just being a jerk, and don't sweat it as much as if my net karma decreased by 20 in a several-hour period but with certain comments being downvoted by 2, certain by 1, certain not downvoted, and certain upvoted.