Check out the discussion at SlateStarCodex about banning Steve Johnson, a time-wasting fellow who wasn't quite breaking the rules.

SlateStarCodex does not have a karma system, though.On LW, time wasters tend to be downvoted swiftly, so they don't really waste much time anyway. If someone who's broadly considered a "time-waster" is nonetheless upvoted, this tells me that what they're posting is unusually interesting.