> There has been an explosive growth in cultures which are interest based rather than location based.

That was a surprise to the architects of Facebook's original infrastructure. Facebook started in 2004 as a service for college students. Most traffic was expected to be with people at the same college, or at least in the same region. So the servers were regional, with relatively weak long-distance connections. As Facebook grew, the load was nothing like that. They had to redesign the system completely.