by researchers at Indiana University pegs the maximum number of friends a user can truly keep in contact with on sites like Twitter and Facebook at roughly 150 people.

Bruno Gonclaves and his colleagues studied the web of 380 million tweets sent by 3 million Twitter users over four years and found that most people start tweeting and increasing their number of Twitter friends until they become overwhelmed and pull back, focusing on contacts they have stronger connections to. The saturation point, as the researchers refer to it, occurs at about 150 friends.

British anthropologist Robin Dunbar as the maximum tally of friends a person ought to be able to handle based on his study of other primates, and he did it in the 1990s, long before Twitter was ever conceived.

Social networking has allowed us to vastly expand our collection of acquaintances and occasional contacts, but when it comes to actual friendships and regular social contact, we're limited in how many we can keep up with.