I just read Matt Kahn extolling Boston as an urban place [http://greeneconomics.blogspot.com/]. Matt and his family were lucky to meet Paul Samuelson in a public place twice within one week.
Matt's experience reminded me of a lecture I gave to my urban economics students some years ago. I was trying to define a city. Among other characteristics of cities I mentioned the sociologists' view that cities are places in which one experiences alienation and where one does not often encounter on the street familiar faces.
Some months after that lecture I was marching down Fifth Avenue in New York City. Suddenly I heard a familiar voice from across the street shouting hello to me. It was a student from my urban economics class at the Technion tickled pink that he found a counter-intuitive example to his professor's ramblings.