Key factors in the design of social services

We are currently working on the development of an interface to support charting collective knowledge, I have been thinking about the key factors that are important in the design of social services. Here is the initial list:

  1. Social object – What people care about together. Jyri Engeström argues that social services that fail to understand and articulate the social object(s) that mediate the ties between people (their users) do not succeed (bibliography)
  2. Strength of ties – How strongly people care about one another. Ties can be weak, strong or temporary
  3. Familiarity – Do people know about one another’s existence, are they networked with one another
  4. Similarity – How similar are people (eg in terms of interest, goals). What do they in common that’s relevant for what they are looking for?
  5. Difference – How different are people? What aspects are different that make it relevant for people to know one another or to link with one another in order to achieve what they need. Differences are not sufficiently emphasised in the way social tools currently support connections between people. Focusing only on similarity is problematic in that it reinforces homophily. Identifying similarity is easy, but what would algorythms based on difference be? More fundamentally, would people use a service that recommends them the opposite of what they think they want/expect. And how different can something be before people are no longer willing to even consider it (bibliography)

Any other factors?