Actually, by definition, metagaming is using out of game knowledge. Such as, player that and that did thing such and such in game then and then (yeah, I know, but I won't be using any names), therefore, his role is most likely...

I have no problems with metagaming and actually use it quite a lot. It has proven itself as quite a reliable tactic and it has uses. Nobody plays metagame free, much as they would like it. Some people just use it to smaller extent than others.

Not to be confused with vindicative nature of the players. The two are hardly the same, even if the later can prove useful too. But sometimes you just think people are out to get you. It's not (always) true. Sometimes they are just metagaming.