I would never think of using the "smite" and have rarely given any "karma."
Personally I think for a forum where emotions naturally tend to run high, it isn't really a very good feature to have. A cordial PM (if not public) can be much more effective with less chances of raising hackles.
I suppose Karma isn't so bad though, but still I see it as an atta girl (attaboy) for appreciated like thinking, with somewhat of a political nature.