Several airports in the US (Baltimore, LA, Denver, Albuquerque, and Kennedy) have recently started using these new full-body scanners which utilize (sub-)millimeter waves. This admittedly low-risk radiation penetrates low density materials (clothing) and provides an image of any high-density material in the scanner (i.e., your body/skin). The image is viewed in a separate, closed room for privacy reasons.

The ACLU calls the scanners a "virtual strip search". Now personally, I can see how this technology would be an excellent replacement for strip searches (e.g., in jails or prisons). When a strip search is already called for, this machine can accomplish (essentially) the same objective in a much shorter time and without requiring personal contact between the searchee and the searcher. However, when was the last time you consented to a strip search at an AIRPORT?!?!?
If they randomly select me for this machine, I will kindly inform the TSA agent that I consider a pat-down much less of an invasion of privacy... How about you???