My understanding of these machines is that they are initally to be used for those unlucky ones who are selected for secondary screening. The theory being that the secondary process would be significantly faster. i.e. no need for the hand wanding and pat downs. With all technology there are definate downsides. GE entry scan is not the quickest thing in the world, but it is effective. Heck they had one at the mall here and it works quite well. They had some explosives (a bullet) and it picked it up.

The backscatter machines are good and bad. Exposing us to radiation isn't good, though the radation levels are suposidly less than you get in 8 hours of flight time. Then there are the privacy issues and the issues of abuse. The latest proposal that I have seen has a program to place blackouts over the genital areas and the breasts for women. The only time a screener would see below that would be if there was an alarm item there. (software programing to determine this). The advantage is that there is almost no place for a person to hide an item of any material on them, short of swallowing them.

The issue will become how are the machines used. TSA has a goal of no more than 10 minutes in line, so until the processing times are fully known, I think these machines will be used for sampling and SSSS and not become part of the regular screening process.