I have read accounts before of people making a lucrative living from earning online video game currency and items and then selling them to other players for real cash.  The Korean Supreme Court has recently legitimized this activity:

The Supreme Court acquitted two defendants in a case related to the legality of using cash to buy and sell cyber money for online games.

The court conditioned its ruling on the fact that the cyber money was earned through skill, not luck.

Supreme Court Justice Min Il-young ruled in favor of the suspects surnamed Kim and Lee.

The two allegedly purchased “Aden,” cyber money in an online multiplayer role-playing game “Lineage,” worth 234 million won ($207,558), which was lower than market price, through game item-trading Web sites.

Then they allegedly resold those purchased items to some 2,000 other players and earned about 20 million won.

Aden is used to buy accessories, cyber weapons and other items that appear in the game so that players’ avatars – characters living in the online virtual world – in the game can gain more power.

Currently, 100 Aden can be purchased for 8,000 won through game item-trading sites.  [Joong Ang Ilbo]

As long as they pay taxes I don’t see what the problem is?