This is an interesting article about how players of Ultima Online used the bugs in the game to add new market dynamics:
Our wisdom was not in inventing an awesome cool collectible feature. It was in surrendering control to the awesome power of emergent behavior. The credit we can take is only for having created a fertile and dynamic enough environment where this sort of thing can happen. Environments like this also produce house break-ins (maybe I’ll write about that someday…) and PKing and much else that can be incredibly pernicious. But far more often than you would think, you get magic through serendipity.
Several years ago there was a glitch (a few of them actually) in Final Fantasy Online allowing the duplication of currency. Prices multiplied by about 20 if I recall correctly, in the period of a couple months. The developers banned many of the people responsible removing quite a bit of the money, fixed the glitch and prices plummeted. It was frustrating that I had invested my currency into equipment only to have the currency regain in value.
And thus I learned the power of currency from a video game.
Another interesting one is Diablo II’s economy. It’s mostly barter based because the in-game currency is practically worthless. Interestingly an online forum (d2jsp) created it’s own currency (called forum gold) which posters can trade for items in game. The forum gold is used in other online games as well. You can earn forum gold from selling items in Diablo II to buy items in World of Warcraft which probably makes it the first cross-fantasy world economy.