To be fair to the OP he's talking about these specs
Google Glass - What It Does
which are hardly close to the certified military or civilian HUD which are certified for use in aircraft at the moment.
It's hard to tell from this promotional video how much of your vision is actually taken up with this projection of sharing what you're seeing, and I would imagine that like a mobile phone at the moment it could suddenly pop up with a notification which could fill your vision and be distracting in flight.
Also, since from the video it seems to be largely voice controlled, not really sure how this will work in a noisy cockpit.
Seems like a great invention with tons of applications, but probably not the safest thing to be wearing whilst flying a light aircraft and doing aerobatics, but it is quite hard to tell from the promotional material exactly how it works and displays in your vision, ie just in the corner like in the video, or across your entire field of vision like in the other promotional shots.