Anthropologist Robin Dunbar argued some years back that due to constraints of the primate neocortex the number of "friends" or 'stable inter-personal relationships that can be maintained' by an individual is somewhere in the neighborhood of 150, which became known as "Dunbar's Number." Some felt Dunbar was on the mark (perhaps even too high in his estimate) while others have felt that his idea is outmoded or irrelevant in the new digital world of extended human relationships or 'social networking.'
A good, older article (that leads to more links) on the subject here:
and a more recent, less technical piece, by Greg Laden here:
...but I'd actually be tempted to start with these 2 entertaining pieces:
From NPR (employing the company Gore-Tex as an example) here:
and a funny 'experimental' take on the topic below:
....Now, if you would all just be so kind as to favorite this post to your 1150 Twitter and Facebook friends.