I was harassed at the gate on a DL NRT-PDX flight a couple of months ago. Shoe swab and the usual bag check BS, but a bottle of ice tea bought airside wasn't taken away. There was no random/continuous screening; they simply picked on a handful of pax (just about 1/2 dozen when I glanced at the control list) who had SSSS on their BPs (and thus "alerted" on the BP scanner).

I hate these searches with a passion, and have been harassed countless times by NW/DL over the past decade. Oddly, these days my BPs read both "TSA PRECHECK" and "SSSS".