Danah Boyd has an excellent post on why efficiency and reliability are not necessarily good things in a social networking application:
Social technologies that make things more efficient reduce the cost of action. Yet, that cost is often an important signal. We want communication to cost something because that cost signals that we value the other person, that we value them enough to spare our time and attention.
When an application such as Facebook makes it too easy to send a Cause Invitation to 100 “friends”, the invitation starts to look like spam. When it’s too easy to invite 800 people in your address book to Facebook or Linked In or whatever new social network someone dreams up, it feels fake. Why don’t applications developers purposely make it difficult to choose which friends to invite — make people type in each email address or click on each friend’s name.
My prediction for the coming year: we will see more invite-only, closed social networks.