If it were an option (unfortunately it's not), I would like to see the karma work similar-ish to slashdot.org karma.
Every individual post can get voted up or down (but a user can only vote on a post once). And your overall karma is an aggregate of all your posts that have been voted on, but weighted equally. i.e. if you have 10 posts that are voted positive, and 10 that are negative you end up with neutral karma even if one of those posts got a disparate number of votes one way or the other. It would make it so you would have to be consistently good, or consistently bad to have your karma swing one way or the other. I would still keep votes anonymous though.
slashdot's scheme is becoming less useful. there are more visible messages that are "5; funny" that I don't need or care to read and on the other side of that, useful information and comments often gets hidden (because it disagrees with "group think", etc.) The "group think" problem is a recognised issue with slashdot and I find myself more often looking at all of the comments because the visible ones are meaningless/useless.
But the issue isn't about being consistency. For example, I posted a topic that attracted something like 70 or 80 smites from one or two postings. There was nothing "bad" about them, just that they weren't in accordance with the "group think" of Canon being invincible/the best. And therein lies the problem (i hope what the problem is doesn't need explaining further.)