The Oil Drum

Lineage II was a Korean MMORPG that had a decently sized US market.  They already had segregated Korean servers {which blanket-blocked Chinese IPs).  Over the first year, the adena farmers (common label: $currency farmers) went from highly visible annoyance to a powerful force on the server, with probably around 20-30% of of player hours.  Getting money in the game was an unusually tedious exercise, so there was a major market.

It destroyed the game for a lot of people - I've always wondered what it would have been like without them.  They generally didn't speak english, didn't participate in the social aspects of the game (in a game about blood oaths, not good), and stayed at a low level to farm easy spawns, killing anyone that got in their way.  Then, when the game mechanics changed and higher level players became more valued, the 24-7 farmer contingent became the vast majority of the high level players overnight.  When inflation(always present in fake game economies) killed some of their income, they became contract mercenaries, a major token in the political struggles ingame.

It's not really a sweatshop.  South Korean or Hong Kong pit bosses market and sell the work of numerous Chinese people working out of internet cafes.  I've met people working 3 ppl to an 8 hour shift and 2 ppl to 12 hour shifts, for around $5/day.  In games that are well-suited to scripting, they'll likely hire locally and equip them with the gear, botting programs, etc, but for most games, it's a completely virtual relationship that's performance based (I'll order 100k adena from you a day for $7).  The pit bosses handle the web orders, the delivery, the ads (of which gaming sites that use google ads are frustrated at), and the  pay.  I knew one pit boss that was pulling in $20k/month, I knew farmers who had to camp that spawn in order to feed their family, I knew teen farmers that basically lived in internet cafes, living comfortably, playing socially as well as professionally, and not taking significant income out (one aspect of sweatshop / company town work).

But physically, most of the workers were never under any more compulsion than you can be sitting in an internet cafe, working on a cash-up-front basis for someone in another country to export to still another country.