Well, if you hide Karma but still use it in the ordering of the thread then Karma could be derivated.
In a day you could extract the data from the posts and build a kind of karma-book with top users etc etc...
Roughly, perhaps - you could obviously tell that one thread is more popular than another because it's on top, and maybe in some cases determine that one poster has more karma relative to another based on the way a thread reacts when it's known that they downvoted (since I believe but may be wrong that downvotes from higher karma posters are weighted more._ But factors other than just karma determine the sort order of the threads, and where stories wind up on the front page. How much can you really determine on a site with as much direct moderation as here?