I've got a situation about to come up in my game where I'm considering using Meta-gaming as a tool.
My PCs in my campaign are barbarians, quite suspicious of sorcerery. They shun it.
Last time we gamed, the PCs found a stash of ancient items--a sword like they've never seen before; a steel chest plate--torso armor; and a necklace, all three items sporting the same ancient symbol.
In the PC's village lives an old hag--an Oracle. Most of the barbarians shun her, but she is allowed to live our her days among the villagers. Their honor will not allow them to turn out an old lady into the wild to meet her death, weird dealer in socererous things she may be.
My players are good role players, but thinking ahead as a GM, I want to try to keep the origin of the new items secret for a time longer in the game--to build up the mystery.
Still, if the player figure out something plausible that will work, then I'll allow them to succeed. I'm not the type of GM that will bar something by straight GM fiat. I always reward smart play, and I'm happy to change my storyline to accomodate players who find success.
To instill some of the fear the Barbarians will be having in the players' decision to approach the Oracle or not, I'm thinking of telling the players straight out that if they do this, then the Oracle will require some of their experience points in order to conduct her spells. The Oracle will suck their lifeforce for the power she needs to find the answers.
Now, this is really not true at all. If a player, in spite of thinking that his character may lose a level or several hard-earned experience points, still wants to approach the Oracle and learn about the items, then, in my book, that barbarain has just conquered his fears of the sorcerous unknown.
There's a famous incent from the making of the African Queen, back in the 40's. Director John Huston wanted to get realism in Humphrey Bogart's face as Bogart waded through chest-deep water to pull his boat through a section of shallow river.
According to the tale, this was shot on a backlot in Hollywood, and Huston wasn't happy with Bogart's performance. The director wanted more trepidation when Bogart's character got into the water.
So, Huston put real, life leaches in the tank with Bogart. And, when Bogart realized this during a take, Huston got his realism as Bogart wasn't acting but really feeling what Huston wanted to show.
When I consider my uses for Meta-gaming, I think along the same lines as Huston.