According to this article, the NYPD is considering implementing a video surveillance system around lower Manhattan that would track hundreds of thousands of people per day. The video surveillance system is referred to as a "ring of steel" and is modeled after the system used in London's financial district. There are already thousands of cameras in place in NYC:
New York cops already have about 1,000 cameras in the subway, and 2,100 more should be in place by 2008. Police Commissioner Raymond Kelly strongly backs the increased surveillance, along with the 3,100 cameras that are up and running in city housing projects. Security cameras at office buildings and apartment towers also train thousands of lenses at unsuspecting New Yorkers and often provide invaluable aid to cops.
Apparently the impetus behind the installation of the "ring of steel" was the London terror attacks last July:
New York cops became more aware of the value of London's "ring of steel" during the terror attacks of last July 7, when the cameras quickly provided images of suspected bombers.
What I find interesting about that statement is that the video surveillance system in London didn't help to prevent the attacks, but simply helped to identify and round up suspects after the attacks had occurred. If we must erode our civil liberties in the name of terrorism, shouldn't the primary goal be prevention?