There's Gold In Them Thar Games
Via Terra Nova, the New York Times (reg. required) has a piece discussing the increasing trend of players making serious money off of MMOGs. They cite one gentleman who is able to pay his monthly mortage thanks to his daily ventures into the virtual spaces of Second Life. From the article: "Mr. Ainsworth, 36, was not a fan of online games until his 10-year-old daughter became interested in The Sims Online. He then noticed that a large number of simoleans were for sale on eBay. 'I started hearing about players leaving the game who were selling their assets...so I figured, buy low, sell high.'"
Second Life may well be possibly the only game he could do this in.
Most likely because noone cares about it, and the market for its in-game currency and commodities is tiny.
Any game which has a larger audience (WoW, SWG, Lineage 2, Guildwars, EQ2) would have seen its slew of dedicated "farmers" from Korea, China, India and various parts of SE Asia.
Either with sweat shop labor or automated with bots, they farm in-game currency and items and sell them at a far lower price than anyone in more developed countries could, whilst still maintaining it as a worthwhile time investment.
Some may argue that "You're getting money for playing a game!" but in reality, its no more fun than flipping burgers, or clocking your mundane 9 to 5, its work.
Farming in these games is all boring tedious work, and at the rates being offered by botters and farmers in less developed countries, its not worth doing.
As an aside they have totally destroyed the in-game economies of most of these games, which is generally why the sale of in-game currency is in violation of the Terms of Service.
i made some 3d content just for fun for mmog http://www.there.com/, one item was so popular i made about $3000 AUD off it... and through 3rd party web sites was able to turn in-world currency back to real dough :)
It's probably worth pointing out that although the SL platform itself is not a game, it does host many resident-created games within it's architecture.
Since residents can use a scripting language to program the behavior of the 3D objects in SL, they have taken advantage of this to build a variety of games. In fact, I think there is currently a game developer competition going on at the moment.
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My favorite game in Second Life is Primtionary. Objects within Second Life are constructed out primary objects ("prims" for short) based on several basic shapes. Primtionary is like Pictionary; the contestant is given a word and must quickly construct a 3D model while other players try to guess the word. LOTS of fun. More than worth the $10 I've spent on Second Life so far. That's what I like about Second Life right now; you can spend $10 and have complete access to the game. If you decide to own land and build on it, then you can upgrade to a monthly account. Meanwhile, you can practice building in the sandbox regions and get good enough to build something meaningful once you do decide to upgrade. And nothing prevents you from making clothes, vehicles, pets, etc and selling them while still landless.