I was watching CNN, and a talking head (who happened to be a former Somebody in Israeli aviation) was making a point that I thought was quite reasonable. He said that it's too hard to focus on the method of making explosives, since explosives sufficient to destroy a plane in mid-air can be made from a variety of chemicals. It was more important, in his view, to focus on the people executing the missions; it was much harder to hide oneself from an acute observer than it was to hide chemicals.
Israeli immigration is notorious for doing exactly this; I've never been to Israel, but colleagues tell me of being interrogated to within an inch of their lives about the details of theorems in the papers they were presenting. After 9/11, I remember similar arguments being made in the US, but they quickly got bogged down in issues of racial profiling, and we quickly found that randomly pulling out gentle Caucasian grandmothers from Iowa was a reasonable thing to do.
So what's the computer science angle here ? If we think of computer security, I'd argue that many of the discussions revolve around blocking techniques: this attack on that cryptosystem, that weakness in this OS, and so on. It seems like the security precautions being put into place on the airlines now are just like that: a weakness is revealed, a (usually overblown) patch is put in place, and so on.
This approach appears completely unsuited for protecting against "real" security hacks though ! The much-derided 'humint' approach appears to be far more effective (and far less overtly intrusive to the population at large).