A study by a student at the University of Minnesota suggests that gold farmers - the unscrupulous salt mine workers of the MMO world - have a lot in common with other undesirable lots, like drug dealers and street gangs.
Muhammad Aurangzeb Ahmad, a PhD student, compared the structure of a group of gold farmers with the structure of a group of drug dealers and gangs as part of a wider project on the practices of gold farming.
It's heavy on jargon, but the gist is that gold farmers behave in the online space a lot like drug dealers do in the real world. Namely, aside from being very shady, they're very selective with who they do business with, will often do business with other like-minded individuals, and rely on middle-men to conduct their more far-ranging activities.
The rest of his research, conducted within Everquest 2, is just as interesting, showing that while the bulk of gold farmers are as you'd expect Chinese players, it's unfair to automatically assume all Chinese players are farmers, as most are not.
It also breaks down the typical behaviour patterns of a farmer and provides a brief history on the practice, so if you've ever wondered how these people chug along under the radar of administrators, have a read at the link below.