Many people, including many people on this site (and, yes, including myself) wouldn't think twice about plugging into an available port if they need a charge. Maybe I don't plug into an unlabeled port in some random location where it doesn't look like it belongs, but honestly I wouldn't think twice about charging at a designated area at a conference.
(Though, yeah, I'd avoid a lot of "normal" activities if I ever attended BlackHat.)
(Though, yeah, I'd avoid a lot of "normal" activities if I ever attended BlackHat.)