There's metagming, and then there's metagaming.
In the Deadlands game I run, there's a pretty clear line between character knowledge and player knowledge.
In a Star Wars game I play in, it is sometimes a bit more of an issue - a couple of the players are rather steeped in Star Wars mythology, and tend to assume that their characters know whatever they do, regardless of their skills. This is an issue in that one of the players is *not* steeped in the mythology much at all. She saw the original trilogy once, when she was a kid. So, the difference becomes readily apparent.
There's also the not-evil form of metagaming, in which the players use not the detailed rules knowledge, but the knowledge that they are people at a table, and they're playing a game of a particular genre, so that other players and genre-appropriateness feed into their decisions. This is common in my Deadlands game, and less common in the SW game.