So far, I've only once reached for negative karma and that for someone who didn't even bother to read a few posts and understand what it was about, but his entire post was focused only on the title. Each of us can subjectively evaluate what is a good or bad post for him, but I think that negative karma is something that should be used to warn members when they constantly do something they shouldn't.
Considering that I am not one of those who like to punish people in any way, I will always apply negative karma only as a last resort.