I think this is a subtle but very overlooked point. Geeks are projecting "augmented reality goggles" onto Glass, as if they are going to be feeding you some ongoing internal backchannel of information as you are in the middle of a conversation with someone. Really, it will be much like if there is a TV behind the person. Its rude to be staring off to a TV in the corner of the room when someone is talking to you, and so it will be rude to be staring at your Glass screen when someone is too.