Forcasting 2012 virtual goods market.

http://techcrunch.com/2011/12/07/us-virtual-goods-market-to-hit-2-9-billion-in-2012-with-facebook-games-maturing-mobile-booming/

http://www.business-and-management.org/download.php?file=2010/5_1--14-29-Hamari,Lehdonvirta.pdf