From the Jargon File's entry on the word troll:
To utter a posting on Usenet designed to attract predictable responses or flames;...
Any and all "Troll" moderations will be metamodded by me as "Unfair", as it is impossible to know the intent of the poster. Similarly, all "Flamebait" moderations will be metamodded as "Unfair". How do you know the post isn't stating the poster's actual opinion?
A secondary issue is that polite, sensible postings will often receive the "Troll" or "Flamebait" mods. Knowing the intent of the poster is the primary issue, which renders these moderations meaningless in any case, but these mods are often applied to calmly-stated and thoroughly-reasoned posts that don't even pass a deskcheck for Troll- or Flamebait-like qualities. In these cases, the best guess is ignorance or stupidity on the part of the moderator; in a worse scenario, I suspect political motivations.
While I don't have an out-and-out moratorium on "Offtopic", "Redundant" and "Overrated", I feel it's more important to promote good material; I start off against these mods. (I was inspired in this by someone's journal entry; I'll post a link here when I locate it.) Also, "Offtopic" and "Redundant" are more often dunce caps for moderators who can't see relevance or distinction rather than accurate labels for the comments.
Positive moderations I judge on a case-by-case basis, but my experience is that I seldom metamod these down. I judge these as "Unfair" perhaps one time out of ten.