And that is one of the reasons why so many here are angry. It was a waste of millions of dollars and manpower (not just in the US) to buy those things. There is corruption behind it too.

The TSA has not released any official figures that I can see. Germany ran a six month test at HAM (voluntary use only) and there have been reports almost weekly about why the scanner is a failure.

1) it does not detect items under folds of skin, or hidden around the body. The ZDF television program featuring Werner Gruber is perhaps the most simple but startling example of this. Here is a Youtube video - click on the red circle to see the English subtitles http://www.youtube.com/watch?v=idICUSiGcqo Before the scanner came into common usage, there were claims that it wouldn't detect things hidden amongst folds of skin ie under breasts, or under folds of fat. While Mr Gruber is now a large man, and there is a little joke about it in German when they put on their coats, he doesn't in this example even use his body fat to trick the scanner.

2) the scanner creates a 'false positive' because it cannot see through 'folds or pleats' ie layers of clothing. That could be a shirt tucked in, for example

3) the estimate given by German officials is that 75-90% of those scanned during the test phase required a physical check to resolve the issue

This is the 'safer' MMW and not the backscatter machine; change to backscatter and the story gets worse. That was just a quick summary from a government test more open that that in the US, but you can see why there are so many concerns. And we haven't even talked about health or privacy, just that the machine doesn't make us safer.

Also want to point out that there are many reports of the TSA screeners being unable to spot the dangerous items as well...