Free Team Fortress 2 turns 20 to 30 percent of players into payers

Newell alluded to the average number of social gamers that pay for in-game items and boosts. Calling it a fairly recent statistic, the Valve CEO said that's far larger than games like, say, FarmVille experience. "We don't understand what's going on," Newell said. "All we know is we're going to keep running these experiments to try and understand better what it is that our customers are telling us."