Any cafe that's popular enough to be filled up will have a network of regulars. Regulars chat, share books, go out for drinks and, among the programmer regulars, chat about startups, collaborate on projects or hire one another for contract work. You'd probably not be able to recognize it if you go in and people are all reading and on laptops at the time, but if you start frequenting it you'd start to pick up on it.
When went out of town for an internship a few years ago, I was a very frequent patron of a couple chain shops near the office and one independent shop downtown. I could work on personal projects and enjoy a few drinks without being disturbed. I was in often enough over a six month stretch to recognize most of the staff. Even so, I don't remember seeing more than a few repeat patrons, and even they were only around two or three times. I may have just been around at the wrong time of day, but I covered pretty much every time slot on evenings and weekends.