As much as I object to an "Opt Out" mentality, we could make this easier, by ensuring that all Google Glass users adhere to the "Obscuring" policy (does not exist yet).
Basically if you're in a coffee shop and wearing your Google Glass, anyone in that shop who is signed into Google would get an alert that they are in proximity to Glass, and could then "opt out" of monitoring video and audio. The Google Glass wearer's device would then just blur our the faces of those who have opted out (easy, Google already does it for Maps), and subtract the audio from those users (harder to do, me thinks).
Anyone using Glass with an active monitoring device in-play (video, audio) SHOULD be notifying the people around them that they're actively recording them. Not only is this illegal in most states, if you're in on private property (i.e. Panera, Starbucks, coffee shop, McDonalds, etc.), you can be ejected and asked to leave.
Additionally, if someone near you objects to you recording them, or their surroundings with your Glass device and asks you to stop recording, you have to comply, or you can be slapped with fines and arrest for "Unauthorized Recording" (i.e. recording laws of the state in question). You can't record someone nor take photos of them without their consent. Do people do it? Sure, but if everyone starts wearing Glass, you'll see more people banned from public spaces (i.e. private property businesses) for doing so.
Also, since you can't use these devices anywhere near government buildings, public transportation systems (trains, planes, airports, bus stations, bridges, highways), it's really going to be a pain to take the device on and off hundreds of times a day.
As one of my colleagues once said: "This is an example of a good idea, poorly implemented."