Interesting bit from Bruce Schneier's latest Wired article:
Interestingly enough, while the photo ID requirement is presented as an antiterrorism security measure, it is really an airline-business security measure. It was first implemented after the explosion of TWA Flight 800 over the Atlantic in 1996. The government originally thought a terrorist bomb was responsible, but the explosion was later shown to be an accident.
Unlike every other airplane security measure -- including reinforcing cockpit doors, which could have prevented 9/11 -- the airlines didn't resist this one, because it solved a business problem: the resale of non-refundable tickets. Before the photo ID requirement, these tickets were regularly advertised in classified pages: "Round trip, New York to Los Angeles, 11/21-30, male, $100." Since the airlines never checked IDs, anyone of the correct gender could use the ticket. Airlines hated that, and tried repeatedly to shut that market down. In 1996, the airlines were finally able to solve that problem and blame it on the FAA and terrorism.