You still create "invites" and send them to particular individuals. When things happen, you discuss it, post it, splatter it on a ...wall. You "like" certain products, and heaven forbid someone likes you, you hope you both "like" the same things.
It isn't just social networking that has inflamed the desires of cliques among society. It's prevalent in in all aspects of life in the 21st Century. You can blame Snooki, Diet Coke, Calvin Klein, wait...
Marketing. Advertising. The people that know stuff. We must do whatever the people that know stuff are doing. Have you ever stopped to think who knows stuff? Let me open the door to their world. A person in marketing knows how to read people...they know what makes people jump and ask how high. But in the purest form, marketing is simple animal instinct. Whatever gets the person closer to a mate, food, safety, and heightened senses is what will drive that person to purchase, live in, or be involved in that "thing".
Um, I do remember someone once telling me in 2nd grade that I was a mammal. I guess they were right.