One of the things I've noticed about glass is how distracting they can be. A couple of times in the library, in the process of using Google Glass, I have had friends come up and talk to me. While I was able to carry on a conversation, resisting the urge to look up at the little bright screen hovering above my eye proved to be difficult. Not to mention, the person you are speaking to becomes so focused on the glowing cube on your face that they can't remember what they actually came to talk to you about.
Google Glass has been great in aiding in school work and various other activities, but when it comes down to everyone having one, I'm not sure some people would know when to unplug. It's hard enough to get people to set down their phone and actually have a conversation. Can you imagine what a future family dinner might look like?