By way of Terra Nova, I found the Development Informatics (DI) working paper, "Current Analysis and Future Research Agenda on 'Gold Farming': Real-World Production in Developing Countries for the Virtual Economies of Online Games." Quick definition for y'all non-grognards: gold farming is the selling of virtual/game world goods and services for real money. The easiest example is that I play a game, and with my character, earn a whole bunch of in-game "gold," and then sell it to your character for real money. Other types of gold farming include leveling (improving another person's character for a fee) or actual in-game item sales (selling a very rare or powerful in-game object for real world money).
My first "holy crap" exposure to gold farming was in the excellent January, 2003 Wired story, "The Unreal Estate Boom." In it, Julian Dibbel quoted a study that estimated the size of Everquest's GNP (the biggest game at that time) at around $135 million which, per persona, made it the 79th richest nation on earth. Dibbel estimated that the "value" of all virtual stuff in all worlds in 2003 was around $300 million. Now... that's the total calculation of what *everything* inside these spaces would have been worth if it could have been sold for real dough; the study compared what the going rate for in-game gold was, and multiplied that by the total gold value of all items and character accounts.
So... check out the list of countries by GDP from Wikipedia. You'll find quite a number of small countries whose GDP is lower than $500 million. That means that people all over the world have now attributed the worth -- in actual, real dollars -- of a year's worth of virtual/gaming stuff as more valuable than everything Granada produces in one year.
I'm sure someone smarter (and with more time) could figure out what the "unrealized" GDP of these virtual spaces is; meaning, what all the virtual stuff would now be worth if it could be sold. If (and I'm totally making this up) that $500 million, for example, purchased 500 billion pieces of "gold" (a 1,000-to-1 ratio), and there were actually 50 trillion pieces of game gold being used... that would be a 100-to-1 real-to-virtual ratio, giving us a worldwide, virtual GNP of $50 billion. Which is more like the size of Croatia.
[Edit, 08/04/08. I just realized that the above bogus approximation is probably too complicated even for being so crappy. It might be easier to ask ourselves, "What percentage of virtual goods are realized in actual world money." I still don't know, but a 100-to-1 ratio doesn't seem too absurd; that is, for every one piece of gold purchased from a farmer, 100 are generated "naturally" and not sold/bought.]
As I said... that calculation is pretty bogus. But when you figure that a fairly small percent of all the virtual stuff that's generated ends up being gold farmed... a 100-to-1 relationship doesn't seem unreasonable to me.
$50 billion worth of magic swords, character attributes and elvish gold. You may want to have your kid start playing *more* games.