+1 for "What is Karma" . . . call it a vote for an overhaul; two suggestions:
1) One way or another, get rid of negative karma, it's just a dumb idea; it takes all of the worst things about the internet and allows it to fester --- people don't have to add to your reps if they don't like you, but honestly, unless it costs you something to take away from someone else, there are monkeys out there that are going to downvote like a banana is going to pop out of the computer as a reward for clicking it . . .
2) I don't like mentioning other forums, but I'll do it this once since it's a good example. Slick deals has a good system whereby you can only give positive reputation, and how many points you can give depends on:
a) post count -- to start repping
b) how long you've been a member (you get an extra 1 after a year or so)
c) How much reputation you, yourself have
There is also a threshold on how much positives you can give in a 24hr period, and you can't rep the same person twice in a row.
In the end, people shouldn't "LOSE" reputation for saying something valid if someone doesn't agree with them or even if they're just posted something not that smart. If it's bad enough to take away, the person WILL be corrected in a follow up post by one of our beloved experts
Again, just another opinion but it's worth every cent charged for it