I was on AA this weekend for four flights. On all of them they pulled the first person in line for screening.

I also noticed (on at least one flight) that as the boarding passes were read by the scanner it would randomly(?) select people to be screened. I noticed this because the man in front of me (whew!) was selected. The scanner flashed a message asking if the person had been screened. They told the man's wife who was just in front of him that she could wait for him or meet him on board.

I had read some posts a while back indicating that this pre-boarding screening was very thorough and time-consuming. But the screens I saw seemed to be pretty quick--a wanding and a look through whatever carry ons the person had.