Microsoft gained over 400,000 Facebook fans on their Bing fan page yesterday thanks to a single advertisement in FarmVille. The fan page, which grew by five times in size from around 100,000 users to now above 500,000 users, was part of a promotion by Bing, where Farmville users could gain virtual currency by becoming a fan of the Bing Facebook page. The ad was a clever integration, and users could join the Bing page without interrupting their game.

The big question is what kind of quality of fans does this attract? What’s the value of someone that just clicks on the “add as fan” button and then goes back to their game? Bing attempted to convince users that Bing should be their choice for finding tips about Farmville, and that Bing could help them succeed in their game, and while that’s true, how does signing up to become a Facebook fan relate to the activity of searching for game tips? Microsoft answers this question pretty strongly:

Microsoft’s social media team has crafted Facebook updates designed to cater to FarmVille users. Today it sent out an update reading, “Any FarmVille fans out there? Try using Bing to get the most out of your crops and animals.” It links to a Bing search result for “FarmVille animals.” The update drew 585 comments in four hours and 20,000 click-throughs.

20,000 click throughs is nothing to scoff at, and this really highlights the power of Facebook fan pages. When a user signs up as a fan, status updates from that fan page are shown on their news feed, so it gives them a directly addressable audience.  By making updates related to Farmville, they were able to hit their demographic the correct way, and succeeded in generating a great response from users.

The idea of incentivizing users to participate in actions to gain virtual currency has been a revolutionary one for FB, and the big question remains as to how valuable the actions are to advertisers. A recent discussion I had with Offerpal gave me at least a few answers.  Offerpal stated that for their ‘install’ programs, where users are asked to install a different application to get virtual currency, they use special technology to make sure the user who tries the new application stays for a bit before they get the currency.  This filters out people that don’t actually care to engage with the new application.  A similar technique could help on Facebook fan pages.

While this is only one example of a cost per action technique, the Bing example seems to have been a success, leading us to believe that only more will follow.