In a game it is not necessary to carry coin, you can carry lot's of stuff virtually, and the money supply do not have a impact in game's economy like in real life
Take SKYRIM for example, the money in the game is always limited, every merchant have less than several thousand coins, and typically an item can cost as much as 10000 coins
As a result, people do not store coins, they store items in their closet, lot's of items, maybe totally worth millions of coins, those items become a store of value instead, and they become useless in later part of the game play
So, in a game where BTC is applied, since the items can be generated endlessly, eventually they will worth almost nothing in BTC's value
In some games, items can be gifted to other toons. Some players create other toons just for the gifting aspect. My brother is a high level player investing thousands to get his main toons up to snuff. But for the past several months he's invested zero bucks, yet keeps leveling up his main toon, as well on his newly created one. I don't have a clue as to how he does it, but it has something to do with manipulating the URLs. There's only a handful of players in the well-known game he plays that take advantage of this.
For the MMORPG, I think creating an alt-currency backed on BTC could be more interesting.
Instead of "mining", when people play, it generates hashes that are used to solve the blocks. When the block is solved, the MMOCoins could simply appear somewhere in the game. Since those coins can only be used for this game, it creates an autonomous economy. Using BTC directly in the game would make the game economy sensible to external events.
After that, if you want to "check out" of the game, you could simply sell your MMOCoins for BTC and bingo! You played a game and you made money!
Now...why I'm talking on this forum instead of coding that MMO....
Before I even came up to your post, Brunic (are we related?), I envisioned such a scenario, sans the specific MMOCoins aspect.
~Bruno K~