Due to the recent air terrorism attempt, air travel now has additional and varied new security.  I have had a difficult time finding specific new requirements for passengers on the TSA site or on any individual airline site.  This New York Times article talks about a one carry-on bag rule.  It appears that one carry-on includes a handbag or briefcase.  The advice I have seen posted most often is to arrive with a great deal of extra time for your flight.

~mary anne