Glass definitely not, because it's kinda crap (what I've seen so far are phone-style widgets — which I loathe in the first place — and telling your shades to record a video — underwhelming). An actual HUD/Augmented Reality system I can see myself using rather easily (as long as it remains fully under my control), but this'll need severe improvements of image processing and recognition (speed and flexibility).
I don't want notification popups, but virtual/augmented surface display could be very neat, e.g. have buses display "live" in wireframe even when they're outside field of vision (think "wallhack") to estimate how much time I have until it arrives, that kind of things.
Or the ability to "switch in" to an other user of the system (and get direct viewpoint) useful for virtual visits (potentially via "presence" robots, plug into the robot and see through it), helping people with stuff or (the other way around) getting help, imagine a tech of some sort doing an estimate of building/fixing something based on what he sees through your eyes. Also useful for things like surgeries (get colleagues in-viewpoints to assist/warn) or single-person dangerous works e.g. underwater stuff, multiple eyeballs on the same field of vision can pay attention to more things.
Or more "mundane" (but actually more difficult) applications such as ebooks with the physical feel of real books by having a "blank book" and AR inserting the ebook's content on the fly, or hologram/3D AR (easy to do when you've got a display per eye)
Glass if one thinks about it deeply is something unnatural.. microscopes, telescopes, vision impairment correction or shade from harmful sun.. or immersive , time disruptive experiences like a movie.
So the key barrier that glass concept is going to face is user rejection beyond the initial bubble crowd. Average people already have a certain context in which they find artificial inputs acceptable ( TV etc ).
Our distinction between natural and artificial sources of audio is different to visual.
I may be entirely wrong and Google may change the habits of a lot of young kids .. that is actually a rather strange and terrifying thought.
Map overlays, video chat (with a better camera), and of course outright augmented reality.
At some point, the display will be integrated in the actual glass and will be able to pick a different focus distance for every pixel. Add in sufficiently powerful mobile computers, and you have full AR. When that happens, Glass (or its successor) will become truly indispensable; this is just the birth pangs.
Might be a decade or two, though. It's a tall order; molecular nanotechnology could construct a device like that, but I'm not convinced we'll be clever enough to do it before that point.