Glenn Reynolds of Instapundit has a piece in Popular Mechanics about the growing trend of cops bullying photographers who take pictures in public places, and why officials who believe such photography is against the law are mistaken.
I believe there is a good case to be made that having lots of cameras in the hands of citizens makes us more, rather than less, safe. Here's how bad it has gotten: Not long ago, an Amtrak representative did an interview with local TV station Fox 5 in Washington, D.C.'s Union Station to explain that you don't need a permit to take pictures there--only to be approached by a security guard who ordered them to stop filming without a permit.
Legally, it's pretty much always okay to take photos in a public place as long as you're not physically interfering with traffic or police operations. As Bert Krages, an attorney who specializes in photography-related legal problems and wrote Legal Handbook for Photographers, says, "The general rule is that if something is in a public place, you're entitled to photograph it." What's more, though national-security laws are often invoked when quashing photographers, Krages explains that "the Patriot Act does not restrict photography; neither does the Homeland Security Act." But this doesn't stop people from interfering with photographers, even in settings that don't seem much like national-security zones.
Taking Photos In Public Places Is Not A Crime: Analysis (popularmechanics.com, Illustration by Rui Ricardo, courtesy Popular Mechanics)