Like all good ides open to abuse, tick of a guild leader and he/she could, not saying he/she would but tells hole guild to put on ignore, or some one is ticked at so in so, so tells mates to put on ignore.
Well worst case scenario is we keep an eye on someone who's not doing anything wrong. I don't see this as being a problem. Like I said, we are not going to act unless we witness some mis-deeds on our own.
You only ignore someone when that person is being a drag. So doesn't it make sense that a person ignored by many other people has something wrong going on? Also, people in a guild, and I'm speaking for myself, have a mind of their own. If they see someone is not doing things right, they'll /ignore the person. If they have no reason to, they won't. Even if they do, Rayken has mentioned the worst scenario.
I think it could be yet another good indicator for GM's of misbehaviour and it could also point to people who are constantly RPing in an incoherent way, so GM's can give some advise (not ban, kick, mute or warn either. It's just that people don't take people seriously most times.)
I believe it'd make the GM's work even better.
Example:
Imagine player B gets a report filed against him. The GM's check it and they can't make much of it. So they go to the ignore meter and voila! The person has 27 ignores. So the GM's ponder a bit and decide to check out what that person's going on about.