[quote=@Dervish]Like Ammo said, metagaming is a personal problem that any half decent roleplayer won't get caught up in. If it is a problem, the GM needs to step in, simple as that.[/quote]

IMHO, this is correct, but I'd go further and say that not reading along with the RP is a personal problem and show of character. That way we hit both nails in one hit - you get rid of metagamers, and you make reading posts the personal responsibility of anyone involved in the RP.

That way, you also make it so that individual GM's can all have their own idea on whether people should read everything or not.. which we've been doing anyway. 

I think that answers both questions - those related to metagaming (it's a personal problem) and that related to not reading problems (also a personal problem, and one that the GM can have their own approach to.. which is how it's been done as long as RPG has existed).