Most of the changes you see at airports since 9/11 do very little to improve security, considering the cost and hassle. Take for example having to show ID — most of the 9/11 hijackers had perfectly valid US-issued IDs, and were not on any list. Or the futility of the TSA's belief that their watch list (which contains hundreds of thousands of names) will catch terrorists. Once again, most of the 9/11 hijackers weren't on any watch list, and even if they were they simply would have used different names. All the watch list accomplishes is to delay a 4-year old from boarding the plane with his parents.
Amos Shapir made a sad but true observation on the RISKS mailing list:
The newly formed U.S. TSA has a serious problem: they have to supply Security, but they have no idea how (and it seems that they are unaware that nobody else does, either). But they do know that Security causes Harassment, and they do know how to do Harassment. So the obvious logic is, the more Harassment they'd do, the more Security will be produced. QED