MMORPG sweatshops1UP.COM has an article about sweatshops with workers who earn gold in online games, which then sells for real-world cash on Ebay. Cory Doctorow predicted the practice in his short story "Anda's Game". (Salon registration or daypass required)
The practice is fascinating, to say the least. I've always wondered if any of the struggling online games might try to reach profitability by secretly creating and selling gold through back channels. Having an exclusive license to print money in your own game seems like it would be too enticing to pass up.