I forgot where I first read this. It was probably in a book or a blog, but I just checked out wikipedia for the information. I’m just going to copy it here.
Dunbar’s number is a theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is, and how each person relates to every other person. Proponents assert that numbers larger than this generally require more restricted rules, laws, and enforced norms to maintain a stable, cohesive group. No precise value has been proposed for Dunbar’s number, but a commonly cited approximation is 150.
Anthropologist H. Russell Bernard and Peter Killworth and associates have done a variety of field studies in the United States that came up with an estimated mean number of ties – 290 – that is roughly double Dunbar’s estimate
So I guess my friends on Facebook aren’t really my friends.