In my coffee house class, my summary idea is that coffee houses are places where strangers can become acquaintances. Coffee houses are not places for building strong friendships. Some friendships may, of course, grow out of coffee house connections. Indeed, I know marriages that began in coffee houses. But a relationship that is born in the coffee house, and stays there, will not grow beyond a weak tie.
Weak ties are very important in real life. Many good things come from weak ties. It is your weak ties that are likely to lead you to a next job, not your strong ties. Weak ties are best for spreading and bringing you new information.
Malcolm Gladwell has a fine article in the New Yorker on the difference between social networks and hierarchies. Gladwell's core point: "Facebook is a tool for efficiently managing your acquaintances." It is not made of the strong ties that can make a revolution.