I was searched with one around the year 2000, IIRC, at the San Francisco airport. I think it was pretty experimental.
edit: there might have been a similar setup at Orly in France in 1997, come to think of it. The striking thing there was the soldiers with rifles (just 3 of them, but walking around) and the way they searched one of my grandmother's bags when the x-ray showed something that looked like a grenade. (it was glass in a weird shape) They were friendly and had a sense of humor about it, and it didn't slow us down, which all made a big difference.
edit: there might have been a similar setup at Orly in France in 1997, come to think of it. The striking thing there was the soldiers with rifles (just 3 of them, but walking around) and the way they searched one of my grandmother's bags when the x-ray showed something that looked like a grenade. (it was glass in a weird shape) They were friendly and had a sense of humor about it, and it didn't slow us down, which all made a big difference.