There were some threads on this a while back. The general consensus from the TSA folks seemed to be that having yourself photographed was OK (the example was in the context of family filming the screening process as part of their vaction home video--weird from a FF point of view but whatever) but that photographing strangers getting secondary was not OK (privacy/humiliation), photographing images on x-ray machines was not OK (privacy of bag owners and/or weak SSI arguments), and photographing screening technology such as working parts of x-rays and ETDs was not OK (SSI arguments).

It also seemed that TSA had told screeners to back off on bugging photographers after some complaints.