It’s ultimately a math question: are you more likely to find compelling content from the few hundred people in your social network, or from the millions of people posting on the service? The answer is obviously the latter, but that answer is only achievable if you have the means of discovering that compelling content, and, to be fair to both... See more

My general theory of social apps is that they compete on the basis of their network structures, rather than their content formats. The network structure—who sees what—is usually the main driver of value.