And for general screening, they're useful for guidance, but I wouldn't trust polygraphs in any specific instance.
http://www.fbi.gov/congress/congress01/senser071801.htm -- "As there are elsewhere in the Intelligence Community, there will be unexplainable false positives and, as we saw in the Ames case, false negatives. On balance, however, we believe the potential for damage to be done by traitors outweighs these concerns."
There was a thread a while back here on FR about detecting minute thermal changes around the eyes while lying. It's an evolutionary response, the article said, for reflexively looking for an escape route. I'll have to find out more about that; it sounds interesting. It would be great for swearing-in ceremonies for politicians.... Time for bed.
You're going to confuse everyone on this thread.