I went through TSA security twice in the last couple of weeks. Both times I opted out of the backscatter X-ray machine and opted for a manual screening. The first time it was the guy's second day on the job. It was a pretty awful experience. He was clumsy and much too forceful. But the interesting thing is I didn't go through a metal detector, and they didn't check the soles of my feet. Not very thorough.
And speaking of that, when I travelled to Africa last May, I accidentally packed my 10 essentials in my carry on, which included my camping knife. It got through SFO security no problem. Only during transit screening in London did they find it.
Then I read this article about how increased screening in airport just redirects attacks to other locations. So we are paying over $7 billion per year for essentially nothing but traveller inconvenience. How sad.