It's too early to tell what we will and will not be able to do with Glass, but I have have imagined how I'd use it:
1) GPS overlay while driving. I bet some folks will balk at this idea at first, but what's worse, taking your eyes off the road to look at a small screen, or having it overlaid (unobtrusively, of course) over some or all of your field of vision?
2) Access to the Internet is so locked down where I work that BYOD has been the employee's saving grace. I would rock Glass while at my desk as I could interact with the things I want without having to go for my tablet. This, of course, depends on how well I can control Glass by hand. The only time you will ever find me giving voice commands to Glass is on the trail, and even then only when hand commands are simply impractical.
3) Many desktop-based games do their damnedest to trap focus in the game window. It would be easier to do things like look up or track game info within my field of vision. The same would apply by default to console gaming.
IMHO Glass, and things like it, are a natural progression heading towards wetwiring. Mainframe -> desktop -> laptop -> phones and tablets -> wearable -> implantable.