You are on the right track IMHO. What is key is that 'best friends' or 'school friends' are highly contingent and ambiguous constructs. They are not fixed, but rather are dynamic through time–people flow in & out of circles for a multitude of reason–which is very hard to operationalize technically. More engineers & techies should at least be familiar and respect more social theory, not because it represents some 'true' representation of how real social interaction works, but more as food for thought when designing social/technical infrastructure(or as we say in the biz sociotechnical ;). I see echos of Erving Goffman, Harold Garfinkel, Anslem Strauss, and Emilie Durkheim in RWW's description of circles.