The community I am part of, the way we try to deal with meta-gamers is education. As I am a member of a Play By E-Mail group, we function more as a shared story and sometimes it is hard to separate what the character knows from the player. If that fails, some of the ways that we solve it is by having the characters going in character, "Uh...How would you know that?" and/or following up with a private email to the offending player and alerting them of the mistake they made.
I deal with them... with extreme prejudice. cocks shotgun
In all seriousness, though, I usually tell them to try to get into their character's head, and only make decisions on what their character knows. I don't think I've ever had anyone not understand the character-player divide after advising them about it.