My main annual check-up doctor, a famous UCSF internist, is strongly opposed to full body, 'just-to-find out' body scans. He is less concerned by the 50 to 500 times increase in radiation exposure; greater than from an annual X-ray (source Landro WSJ 3-2-2010). His concern is that a full body CT scan often reveals a wide range of anomalies about the individual scanned that deals with the complete unknown. Clusters of muscle and fat appear in the wrong places, dark spots occur that don't connect to any known problem and lesions of all sorts are found that don't connect to any known symptom. A whole can of worms is opened with worms that may or may not be important but lead to worry and further probing expense.
I am reminded of the book How We Die by Sherwin B. Nuland. He is a doctor who was disturbed by the number of prostrate tests that came out positive and led to surgery only to find benign tumors. So Nuland paid for eleven autopsies of Harvard men who died of old age and found that the majority of them had prostate tumors but hadn't died of prostate related cancer. (Here is a similar study.)
CT technology has shown that much of the internal human world looks threatening but because its existence was formerly unknown the relation to health is also unknown. New data, no theory, too bad.