Fascinating read, definitely read it if you are a frequent flier:
http://arstechnica.com/science/news/2010/12/the-physics-and-biology-of-the-tsas-backscatter-security-scanners.ars/Clifs:
- Safety Data has only been compared to current X-ray tech, which isn't completely applicable to backscatter tech
- Small amounts of radiation could penetrate thin skin areas, but generally safe as we experience this every day
- Too many unknowns at this point to give them a 100% pass
- Risk of software failure or machine failure could be a major concern, especially since TSA are not experienced with medical technology
- Occasional use seems to be reasonably safe, frequent fliers should however be concerned until more research is done
