Its pretty popular from what I hear and a lot of the time It isn't sexual. Kids do it to get a "high". The problems arise though when they pass out before they can get the rope loose. Dog leashes are used a lot.
My wife is a teacher and told me the latest thing that kids do now is use something to restrict oxygen flow to induce endorphins that way. Too bad it ends up killing them all the same, one of her old students died that way.