Forbes has an article about Open Source Intelligence, which basically means giving citizens ways to alert government to possible threats and sharing some threat information directly with citizens.
I think eventually tools will evolve that will enable even hunches to be part of the equation. If the way a guy is acting worries a lot of people but they can't put their finger on anything, that might be enough to at least send a cop over for a look.
James Woods actually alerted the flight crew on a flight in August 2001 about suspicious passengers who later hijacked planes on 9/11 and a report was filed with the FBI by the airline. If only we had a system that valued these reports! It seems like a pattern of activity would have been obvious to the FBI if they could only google their own data!