I'm very interested in that sort of business model - selling real or virtual products within a free application.  I remember reading an article last year (<a href="http://arstechnica.com/gaming/news/2009/06/eas-new-motto-please-pirate-our-games-er-storefronts.ars" rel="nofollow">http://arstechnica.com/gaming/news/2009/06/eas-new-motto-ple...</a>) wherein the CEO of EA Games claimed not to mind piracy of certain games which had products for sale in-game.  Many websites and applications seem to be using it to great success - IMVU and the social site Gaia Online come to mind.  Somehow it seems strange to me that users who are so hesitant to buy something outright will pour their money into it when it is ostensibly free.