Originally published as a note on my Facebook page Dec 1, 2010.
No, they're not. There are many reputable sources of information that say they don't make flying any safer. A GAO report prior to the purchase of the AIT scanners said the new scanners "probably would not" detect the "underwear bomber" from Den 2009. The TSA's response to that is "we believe the would". No evidence, just a belief. The scanners manufacture indicates they're not effective at detecting low density materials, including powered, liquid, and plastic explosives.
Here's a Q&A with TSA head John Pistole, in which he either admits the procedures are of limited value, or avoids answering questions about their effectiveness. Of course, he spins it in the most favorable way he can, but a little "reading between the lines", aka, noticing not only what he says, but what he doesn't say/answer will reveal a lot.
In that interview, he also says "We're not in the threat-elimination business. We can't do that, but we can try to mitigate some of them." That's a detail that most people miss, and overlook. Said another way, the TSA knows they can't stop all the attacks, in fact, if you read carefully, "we can try to mitigate some of them" indicates that at best, these procedures might make it a little more difficult for an attacker. Is it really worth giving up your privacy and being subjected to very revealing (and possibly dangerous) scanners or invasive pat downs because "we can try to mitigate some of them"?
Smoke Screening Best article yet on the insanity and uselessness of the TSA approach to security. Security expert Bruce Schneier explains and demonstrates in a US airport just how ineffective the TSA practices are.