In the spirit of "other people learning from mistakes" - our R44 was oversped a good few years ago and the cause was not the common open throttle but the pilot lifting to hover whilst not being completely aware of his surroundings, which introduced excessive yaw, then in an attempt to get to a "place of safety" away from other things pulled in excessive collective too quickly which meant the governor couldnt keep up.
CC
Also seen things heading this way a number of times as an instructor when the student is tense, could be a slow governor (common at altitude) but more common in my experience is the student/pilot is gripping the throttle too tightly, white knuckled, and not letting the governor do it's job.