Coffee shops were the first social networks. They were places to exchange information, to test out new ideas, to banter, and to work.
People use social media today as a way to set up face to face conversations at the coffee shop. Cafes help facilitate discussion by providing just the right amount of background noise, or Coffitivity. Coffee also helps relieve tension by giving people something to hold.
Coffee shops are neutral places, serving to provide safe havens for discussion and bonding. But I guess the same can be said for the bar. It doesn't matter where people meet as long as they always have somewhere to go. Cafes and bars just happen to be excellent public forums.