As of October 18, 2010, thanks to a successful NYCLU lawsuit on behalf of Antonio Musumeci, the federal government (finally) acknowledges that there are no federal laws or regulations prohibiting photography outside federal courthouses. Details here:

http://www.nyclu.org/news/nyclu-settlement-ends-restriction-photography-outside-federal-courthouses

And BTW, it’s also OK to shoot on the subway: NYCT Rules of Conduct on the Official MTA Site – section 1050.9(c). state that “Photography, filming or video recording in any facility or conveyance is permitted except that ancillary equipment such as lights, reflectors or tripods may not be used. Members of the press holding valid identification issued by the New York City Police Department are hereby authorized to use necessary ancillary equipment. All photographic activity must be conducted in accordance with the provision of these Rules.