In an interesting (though somewhat old) paper on the Social Science Research Network, South Korean Judge Ung-gi Yoon argues that despite court cases in his country ruling to the contrary, the trading of virtual property is a practice that should be allowed under the existing law. While developers maintain a legal grasp on the IP rights that govern the ownership of in-game items and currency, Yoon argues that the very existence of trading within the game grants players a tacit right to exchange in-game items. And moreover, since what is being traded is really the right to use certain items earned in-game, the ability to transfer this right via RMT can be inferred without much controversy.
The paper is thorough examination of the South Korean perspective on the topic, and deconstructs some oft-held misconceptions about the legality of certain clauses in MMO terms of service. It's a good read.
