From security expert Bruce Schneier’s weblog, and also Wired:

It seems like every time someone tests airport security, airport security fails. In tests between November 2001 and February 2002, screeners missed 70 percent of knives, 30 percent of guns and 60 percent of (fake) bombs. And recently (see also this), testers were able to smuggle bomb-making parts through airport security in 21 of 21 attempts. It makes you wonder why we’re all putting our laptops in a separate bin and taking off our shoes. (Although we should all be glad that Richard Reid wasn’t the “underwear bomber.”)