The frame of mind I have with Glass is to think of problems where the "taking phone out of pocket" motion is inhibitive enough to be a barrier for a successful app.

For example, QR codes today are something that pretty much nobody scans but will be relevant overnight if people start wearing these. Or, any app that is useful for you while you are driving, like parking assistance or finding nearby gas stations.

Also there could be some interesting applications that arise when you consider that if you are wearing Glass software can know when you are looking at a particular display, like your phone or computer.