If you’re beaming it directly into your retina, how can that not be harmful?
James, you’ll find that the light used by the projector is really dim compared to a standard projector. Google Glass probably uses a small projector module from Microvision or a similar company. While it is directed straight to your eye, the amount of light you get is ultimately going to be similar to looking into a LCD, or maybe even less light than that.
What I’m more worried about with Google Glass is the focusing problem: unless they’re being really smart about their optics, the Google Glass image will only resolve when your eye is at a particular focus. Anyone who has used a wearable display for a decent length of time can tell you this gets annoying pretty quickly….