400,000 gold farmers earning an average US$145 per month

Andrew Leonard discusses gold farming on Salon.com.

Gold farming is the term for accumulating play money in online computer games with the intention of exchanging the game money for traditional government-backed paper currency.

Leonard's topic is a new 87-page research paper, "'Gold Farming': Real-World Production in Developing Countries for the Virtual Economies of Online Games" by Richard Heeks of the University of Manchester. Apparently 400,000 folks make their living doing this with a global market between $500,000,000 and $1,000,000,000 for game gold.

(via bOING bOING)

I'm not sure if a numismatist could collect and display game gold. It only lives in the game and doesn't actually have an appearance. Buying farmed gold on an exchange merely means you'll get a game-world visit from a stranger who will give you game money. The game money will merely increase your bank account balance on a server somewhere.