A must read:
“Online social networks are webs of relationships that grow from computer-mediated discussions. The webs grow from conversations among people who share a common affinity (e.g., they work for the same company, department, or in the same discipline) and who differ in other ways (e.g., they are in different locations, keep different hours, specialize in different disciplines, work for different companies).
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Search engines find facts. People provide solutions to problems. Networks of people can solve problems for each other. Online networks accelerate and globalize the process. Each person in a network knows more than anybody else in the network about at least one special interest and can provide useful knowledge when questions arise concerning their area of expertise. No person is an expert on everything, so we must rely on the expertise of others.”