The nuances that make an open source tool like GPG attractive to us are unlikely to make much of an impact on terrorists that believe in vast US/West conspiracies.
I think the biggest mistake the first world can make in securing its future is assuming that it has a monopoly on knowledge, intelligence, and expertise.
Yet several had the expertise to fly commercial airliners. A number of top Al Qaeda leaders went to college in the U.S. It wouldn't be implausible for some terrorists to take courses in computer science.
While I don't doubt Al Qaeda has some skilled technical folks, piloting a commercial airliner isn't much of a feat if you don't intend to land the thing.
Landing in good weather is not particularly difficult. What's difficult is handling error conditions: the landing gear won't go down, an engine has failed, some instruments are out or misbehaving. Landing the airliner, safely, under those conditions require critical thinking, good flying skills, and practice. If you are planning on only taking one flight, you don't need to be good at this stuff, because it's unlikely that you will encounter any problems on that particular flight.
(Lots of people have died because of inadequate training in these areas. Eastern Flight 401 is a good example: http://en.wikipedia.org/wiki/Eastern_Air_Lines_Flight_401. The crew was so busy debugging a faulty light bulb that they forgot to fly the plane. It crashed into a swamp.)
It's probably better for attempting to elude the NSA, as well. Get lost in the mix, as opposed to having big large red flags in your messages.