Share 'What is required for a social network, when you remove the buzzwords?'

Basically the only aspects that differentiate a social network from a more traditional community (forums, message boards etc) are Profile pages and Friends. Is this distillation correct? And if it is, are profile pages and friends really necessary for the uwebd community? Because I have seen a lot of quite successful online communities that did not have either. In fact, a little off topic, but…