How can one breathe the word "viral" and claim to debunk the concept without looking at data from one of the many Facebook apps that actually, you know, <i>went viral</i>? [that's a rhetorical question, I fully realize that the answer is that they don't have any truly worthwhile data to look at]<p>The lone Facebook app in the study is one that the authors made themselves, and it's no surprise if you've never heard of it: while I wouldn't take AppData's stats as golden, they're usually in the ballpark, and they claim Friend Sense maxed out at 317 MAU (<a href="http://www.appdata.com/apps/facebook/7890187783-friend-sense" rel="nofollow">http://www.appdata.com/apps/facebook/7890187783-friend-sense</a>) - to give you a sense of scale, the 2000th most popular app on Facebook had over 100,000 MAU (<a href="http://www.appdata.com/leaderboard/apps?fanbase=0&metric_select=mau&page=50" rel="nofollow">http://www.appdata.com/leaderboard/apps?fanbase=0&metric...</a>). Even under the assumption that it's hard to get solid data on such low traffic apps, it's easy to conclude that no, Friend Sense is <i>not</i> a representative example of a successful Facebook application, let alone a viral hit...<p>I can't give you numbers or anything, but I don't need to violate an NDA to tell you that if you're actually at a point where you're making real money off of Facebook apps, you're almost certainly seeing non-negligible virality, and you should be thinking about it, measuring it, and incorporating it into whatever business analysis you're doing. Your viral coefficient may not be greater than 1 (and if it is, God bless you and enjoy the ride, at least until you saturate!), but trying to increase it is nowhere near as futile as these authors claim - successful apps have network structures that can be very broad and very deep, and most would not have been successful at all without them.