When you use the automated machine, you put your passport in, answer some questions, then you stand and have your picture taken by the machine. If your picture (or the whole paper, I can't remember which) has an X through it, you have to go through a more thorough screening line. If you have no X (which mine did not, but Eric's did), then you go straight through the immigration line. As Eric said, it seemed like almost every family, at least one of the family members had an "x", therefore of course, everyone would go through the "x" line, because they didn't want to be separated. I have no clue what causes a person to get an "x" on their form, but possibly it's totally random. So, if for instance, the machine randomly picks 10%, say, of people to get an "x", if there are 4 people in the family, now there are four people in the random pool, when they only intended 1. I don't know, it would be interesting to hear if it is a glitch in the machines themselves, or whether it is something to do with the camera or what, as to the reason why so many people are getting the 'x'..

There is a video playing on the AA screen before landing and, while I didn't pay a whole lot of attention to it, I believe they said that foreign nationals who had entered the US two times in the past few years could use the automated system..