Last paragraph of the article: "A very interesting variation of this is when you apply Metcalfe's Law not to the entire network of users, but rather think of a social network as a loosely grouped set of connections. In that case, some local networks might have achieved critical mass, and if they are big enough, they will be retained. However, if the smaller networks around any given group start collapsing, then sometimes even the large networks will get pulled down with them."<p>This also explains why some people just "don't get" facebook, while others do; and these two groups have a hard time understanding each other. It all has to do with critical mass.