It helps that the context was threefold: NSA spying, NYPD Stop & Frisk, and NYPD unlawful surveillance of Muslims throughout the tri-state area. All clear 4th Amendment issues. We had a diverse crowd, with a mix of geeks, Occupy-types, Tea Partiers, and members of the Muslim community.
We marched, we chanted, we even took some streets in lower Manhattan. Hard to say how big, but probably about a thousand there. The farthest anyone got off-topic was "Free Bradley Manning." Very rare to see that kind of discipline in a diverse crowd. I was very impressed.