As I mentioned elsewhere, there isn't a good way to enforce no metagaming. I will politely ask everyone to adhere to their character's knowledge and abilities, but I can not enforce that in an unbiased manner.
Metagaming may result in a private discussion with the player, but that will be discussion only. Truly gross and consistent metagaming may result in my asking them to leave the game, but it would have to be both gross and consistent.
As for clever use of magic items: Naw. He could have been told how to do it by a smart buddy. I may nerf it, depending on how abusive of the spirit of the item it is, but I prefer to reward cleverness.
The kind of metagaming I'm more annoyed with is things that the character has no way or right of knowing, like where an invisible person is.