[eridius]

Social media also relies on social graphs to provide value. But a bookmarking service like Pinboard, while having social components, derives most of its value simply from the service it provides to the user on its own without any social connections. Someone who uses Pinboard without knowing anyone else on the service still gets 99% of the functionality that someone who has friends on the service gets. So it makes sense that a site like Pinboard can eventually plateau on the number of users and still remain successful (assuming users are paying a subscription).