Say the Wall Street Occupiers concentrate their numbers on a few city blocks as tactical and organizational necessity would predict. Based on these numbers they would account for about a 15% increase in population but only in the area that they occupy—well, maybe, because my calculations are rough and based on Wikipedia numbers, and on any given business day the population of New York City’s financial district increases to about 300,000 workers. So in the mornings and afternoons when most of Manhattan rises to its feet to travel along the sidewalks to or from the bus stops, train stations, or parking garages, the Occupier formations would hardly rise to the threshold of most peoples perception unless the Occupiers got deliberately in the way of pedestrian traffic. (This, however, I would notice immediately.)
Here be the numbers of Occupy Wall Street protesters by location as reported by the Washington Post in the form of a table.