There is an interesting piece in the Atlantic's Cities: Place Matter site about walking and eye contact with strangers.
The article cites a study involving an experiment where a woman on a college campus either makes eye contact, smiles and makes eye contact, or stares right through a fellow passing pedestrian.
Within a minute of the interaction, a second study member would ask the passing pedestrian - unaware that the eye contact or lack thereof was staged - a series of questions on how connected they felt to society.
Not surprisingly, pedestrians who had received eye contact reported the highest sense of connection to their community. Those who had been stared right through had the highest sense of disconnection (and higher than the control group).
The Atlantic Cities author conducted his own experiment in Washington, DC on his walk to work. Only 12.5% of people acknowledged his attempt to make eye contact. From my experience walking around Portland, I think the rate would be higher here.
Of course, there are many reasons people might not want to make eye contact with strangers, but in general, Portland is still a pretty friendly place. One of walking's great attributes is the ability to enjoy your surroundings and experience the place as opposed to simply going through it.
Graph courtesy of Eric D. Wesselmann, Purdue University.