Emerson Larkin, 23, just reaped $400 selling two characters for Blizzard Entertainment's "World of Warcraft" after investing nearly 75 online gaming hours creating them. Some big name corporate players have started to get into the business of virtual asset trading, which is so hot that some industry experts say it may be overheated.Still, virtual asset trading has a long way to go before it rivals eBay's multibillion-dollar revenue.