Last year, while travelling on Air Deccan, a low-cost airline in India, I carried a pocket knife onboard the airplane.... The story is far more interesting than that summary alone, and I highly recommend you read the full writeup here:
The photographic evidence of the event is here:
A knife on the plane:
Sealing the locks to prove that they haven't been tampered with:
However, that was India - and this is America... land of the free, home of the brave - and more importantly, home of TSA - who is supposed to be protecting you from big bad terrorists.
It's common knowledge that a tiny fraction of the checked luggage (which is just a few feet below the passengers in the airplane's hold) is actually x-rayed.
On top of that, it's also common knowledge that the airlines only perform passenger matching on bags for one airplane trips: i.e. if you don't get on the airplane on a trip from Indy->DC, then they pull your bag off at the last minute. However, if you get on the airplane from Indy->DC, and then leave the airport instead of getting on your connecting flight from DC->San Francisco, they let the bag go on the next flight. A terrorist would simply put a timed bomb in their bag, and have it explode during the second flight.
However, lets ignore those facts for now.. and focus on what TSA is supposed to be good at... keeping liquids, nail clippers, and weapons out of the airplane cabin.
My girlfriend visited me this weekend, and accidentally left a sharp paring knife in her carry-on bag.. both ways (i.e. DC->Indy, and Indy->DC). It was only once she got back to DC this evening that she realized what happened.
And guess what... TSA didn't notice at all.
For the record, as much of a troublemaker as I am, my girlfriend wasn't trying to test TSA. She is a law-abiding citizen, and simply overlooked the knife in the rush to pack her (messy) bag for her flight....
The evidence is here: