This also brings up other interesting issues. In the US, you aren't allowed to mint your own currency. For example, you can't put $100 in the bank under a special account, and then mint $100 remybucks, give them out, and say that you'll exchange remybucks for dollars. Places like DisneyWorld get around this because their special currency never leaves Disney. There is no exchange rate.
The Federal reserve is notoriously picky about competing currencies. As sites like GOM start replacing eBay as the place to exchange your game-money, and game-currency trading takes off, this might become an issue. Maybe. It's hard to say, because I seriously doubt anyone is going to be buying grocieries with Simoleans. However, people do make money with GOM.
The whole phenomenon is interesting though. People log into a game, and perform simulated labor. They make items for other players, and kill hazardous creatures, and in turn, are rewarded with gaku (game currency). Now, gaku is usually turned in for game items, or favors from other players. Gaku was never meant to leave the game. However, the motivation for it to leave is obvious. In the game, you can make fabulous amounts of gaku. More than your character can ever spend. And most game systems have a method to keep you from giving excess gaku to other characters you control. Maybe though, you haven't been so lucrative in Evercrak, but have raked it in while playing SWG. Or maybe you want to start a new SWG character on a different server, and be able to give that character a boost. Or, maybe, you run a TSO brothel, and are using it for income.
It's interesting to watch how the abstraction has grown. Originally, people would sell Evercrak items on eBay. That's fairly concrete in net-terms. It's an actual item that performs a function. Mind you, it only exists on Evercrak, but nonetheless, it's fairly tangible. Gaku is an abstraction that represents those items. That's what all money is; an abstraction that represents real-world goods and services. Now though, instead of trading items, people are trading what represents those items; gaku.
I think the biggest thing game companies are going to have against things like GOM is that they screw with the game balance. A player can go to GOM, sink some money into currency, and start their character off with lots of money.
Amusingly though, one of the biggest challenges GOM predicts is a problem with inflation. Gaku is an inflationary nightmare.
It's just so strange...