How much is a Facebook Fan worth?

Microsoft’s recent FarmVille promotion grew Bing’s Facebook fan page from 100K fans to over 500K fans in 24 hours and gave away 1,200,000 Farm Cash dollars in the process. Each participant in the promotion was rewarded with 3 Farm Cash dollars for becoming Bing fans on Facebook.
Some of the most desirable virtual goods are sold only for Farm Cash. Farm Cash is earned in the game at a very slow rate but players can purchase more Farm Cash using Facebook credits, credit cards and Paypal, as well as alternative payments like Zong (mobile) and Offers. Players get discounts on Farm Cash for buying in bulk. The best deal you can get from the FarmVille app is 310 Farm Cash dollars for $50 USD, or 16 cents per Farm Cash dollar.
At that rate, Microsoft valued a Facebook fan at $0.48 and would have spent $192,000 on the campaign. However, it’s likely Microsoft received a huge discount for such a large buy. A social gaming insider told me today that Microsoft paid $0.10 per unit of Farm Cash. At that rate, Microsoft set the value of a Facebook fan at $0.30, paying $120,000 to acquire their new fan base.