People seem to be on either two sides of this. For the people who argue that everyone carries a camera in their cellphone and could be recording you, or that anyone can buy a cheaper spy camera, here is my argument for you.
This is obviously a extreme parallel I am about to draw, but I am going to compare Google glasses to to guns...
I see the arguments being very similar (in the US). People can legally (in several states), carry guns, even concealed ones. This is bad enough as there are people who feel uncomfortable if they just saw someone carrying a gun in a holster. Now my comparison is that what Google Glasses is doing is that they are taking it one step too far. They are basically doing to equivalent of allowing the person who carries a gun today to basically walk around with it, holding it 24/7 in a shooting position (arms straight out, finger on trigger). This would obviously scare the living hell out of most people if someone was holding a gun this way in a bar.
This is effectively what they are doing with a camera now. Yes everyone has a camera on their cellphone these days, but most of the time its in peoples pockets or bags. And if it is out it is either pointing to the floor, to a table or towards a friend if you are taking a picture. People dont walk around with their phones out 24/7 and pointing it faces of random people in bars. Yes someone could sneakily film someone by holding it in a subtle way or by using a spy camera. But someone could also hold a concealed gun under their jacket and have it pointed it towards you. Just because they can do that already, doesnt automatically give them the right to walk around with it pointed towards you at all times.
My point is not that cameras == guns. My point is that the step from having a camera on a cellphone in a your pocket to wearing a camera in your glasses is the same length step as going from carrying a gun in public to carrying it whilst pointing it straight out in front of you.