I’ve got a tip for the Google guys working on the project glass.
Try to make it as transparent as possible. People don’t like to be’ distracted while doing something important.
**Follow eyes movement **
As doctors already do every day in hospitals google can integrate a system that can follow your eyes movement to make UI elements transparent if necessary. With nowadays technology it can’t work perfectly, we’re not there yet, but it’ll be still better than the actual ones.