If you saw a flock of naked or near-naked bicyclists, it wasn't your eyes, it was simply the Second Annual New York City World Naked Bike Ride. According to its website:
Naked on a bike is about as free as you can be! This ride is majorly fun! This year's WNBR is supported by a generous contribution of outrage from British Petroleum. BP is unleashing incalculable devastation upon the environment and livelihoods of people in the Gulf of Mexico, while the government is unwilling to reign in the corporate culture that led to the spill. WNBR is a chance to put your beautiful body to work against this calamity, which is a direct result of OUR dependence upon fossil fuels and automobiles. Exercise your rights to bare your chest in NYC, your rights to assemble and to protest, as guaranteed by the US Constitution. Nudity is not requisite, please join as "bare as you dare" and use your body and bike to create the massive numbers needed to make this effective.
The ride (and body painting) began yesterday afternoon in Grand Ferry Park in Brooklyn and then headed into Manhattan. Also noted on the website: "WNBR should be a fun experience. We're out to create a little joy and justice, but without justice, we can't have any joy. So make sure you respect the self-determination of each rider," as in, "Ask before photographing, videotaping, touching, staring at, falling in love."
FYI—the gallery of photograph is pretty SFW (there are shots of some bottoms and body-painted breasts, though).