There are obvious times with the random aspect lands on a non-starter. Infant tickets, 80 year old grandma from Wisconsin, etc. Completely unecessary screenings.
There are also pretty solid statistics on age/sex profiles of suicide bombers and some pretty telltale signs.
[link|http://www.nytimes.com/2005/07/28/opinion/28sperry.html?ex=1280203200&en=4cc1386247dcd8f0&ei=5090&partner=rssuserland&emc=rss|http://www.nytimes.c...suserland&emc=rss]
Our problem is that we can't keep our collective mouths shut. Of course, if we establish a profile, we will be compelled to shout it off the highest rooftop so that everyone knows EXACTLY what we are looking for...and then it will obviously be a damned simple exersize to subvert.