One of my companions was nude-o-scoped at the South Security full body scanner recently. It did seem completely random, which sort of defeats the object doesn't it?
I also got "done" in HAM recently, where despite picking the non-nude-o-scope line, I got directed back into it. The security staff at HAM were also the first to request that my Kindle came out of my bag... And if you didn't consent to the nude-o-scope then you got a full pat-down.