rdf technology is coming on strong in late 2011; the tools are getting better fast -- we will be able to represent the social graph in more detail, and correlate it with the 'semantic graph' that shared human experience is coded in. yes, RDF has taken a while to mature, but look at the time lag between Codd's paper and the commercial release of Oracle. 1000 flowers have been blooming for years and we know a lot about…
Many things can be usefully represented by graph structure, and RDF is a way to do that (a verbose and clunky way, but better than no standard at all).
Whether social relationships are one of those things is a separate question.