Backing up a sister comment on this thread: I've lived in SF and Chicago, both also as walkable as it gets for the US, and in both had relationships as a "regular," whether at a corner store, cafe, or the grocer. I remember our Albanian corner store guy in particular, who would comment on me gaining or losing weight. Our neighborhoods felt like a small town where we all knew each other (including the homeless!).

I live near New York now, and while I hear from friends that they find that kind of community in some faraway boroughs of NYC, everyone in Manhattan reports your profound and deep sense of alienation from their fellow man, though some with a positive spin.

I have not seen this alienating anonymity in any other part of the country, though I have felt it whenever I'm there. As there is no other place in this country even remotely as dense or with faster turnover (not even SF), I'm fairly confident Manhattan is unique (in this country).