What's interesting is that all the hype surrounding the explosive viral growth for Facebook apps such as iLike doesn't acknowledge a possible cost. Acquiring 4

What's interesting is that all the hype surrounding the explosive viral growth for Facebook apps such as iLike doesn't acknowledge a possible cost. Acquiring 4 million users isn't strictly additive, if it comes at the cost of cannibalizing your existing Web site visitors. At first, I thought that iLike would only be able to monetize their Facebook users by driving them to their Web site. So, a big drop in Web site traffic seemed disastrous. However, I see now that iLike is showing ads on their "Music Challenge" page within their Facebook app, so driving traffic doesn't seem necessary. (I'm assuming iLike is collecting this advertising revenue. Please correct me if I'm wrong.) That's the real question then: How easy is it to monetize Facebook users? Is a Facebook user (who never visits the iLike Web site) just as valuable to iLike as a Web site user? If a Facebook user is less valuable, how many more Facebook users than Web site users would iLike need to come out ahead?