Perhaps not, but you can calculate the chance that a given customer will refer a friend, and factor that into their lifetime value. Even more interesting, you

Perhaps not, but you can calculate the chance that a given customer will refer a friend, and factor that into their lifetime value. Even more interesting, you can see which actions are predictive of referring friends (e.g., leaving a comment on the suggested features list). You can use the same strategy to predict the conversion rate from free to paid.