One word: spambots.
Maybe we could use the same mechanism to protect LW wiki from spambots. The wiki registration page would be available only to people with karma at least... well, 1 should be enough. Reaching karma 1 should be trivial for any LW member, and pretty difficult for a generic spambot.
I'd like to see, beside the cumulative karma as it is now, also its analytic. Does my 0 points somewhere means no upvotes and no downvotes or +7 and -7, for example?
A timeline graph would also be appreciated.