I think it could increase the value of the karma system, I am seeing a lot of downvotes that I can't explain or that I find unfair. I am also seeing excessive points on some comments.
2) Not related : if you browse someone's comments you may encounter truncated posts titles :
12 points by pg 1 hour ago | link | parent | on: Announcement: YC alumni will help us read applicat...
It would be nice to include the full title in the "title" attribute of those links.
I assume that was your intention ?
This in turn will give the few people that are very active lots of voting power.
The karma here is not so much 'quality' (though that is a component) as much as it is an odometer.
The main point is to force people to be more cautious with their upvotes and downvotes. My theory is that if you have to pay from your reputation (your karma), you'll mainly upvote/downvote what you're really convinced about.