Via Broken Toys I learned about this academic paper on gold farming. 87 pages of research, with interesting estimates, like for the number of gold farmers (400,000) and gold buyers (5 to 10 million). The paper covers everything from the description of what RMT is, to legal aspects, to discussing gold farming as a transfer of money from developed to developing countries.
What it fails to mention is that gold farming is a result of bad game design. Gold farming means that some regular player finds some particular activity in a MMORPG so boring, but necessary, that he is ready to pay somebody else to play the game for him. And that is pretty extraordinary in the field of entertainment. Nobody pays somebody else to go and watch a movie for him, or to go and shoot a couple of hoops for him in a friendly game of basketball. Nobody buys a highscore for Tetris, or an advanced save game for Grand Theft Auto. In nearly all forms of entertainment and games, the spending of time is the *purpose* of the activity.
At some point in the future somebody will discover how to make a MMORPG in which all parts of the game are fun to play, and there are no parts to "grind" to achieve some result of virtual currency or level. And that game will have no gold farming. Not because it would be impossible, or because of being threatened with bans, but just because it wouldn't make sense to pay somebody else to have all that fun for you. The impotent rages of game developers against RMT are really just a reflection of their own failure to make their games fun in all areas.