Useful for what? This is what I'm wondering about.
I read this engadget review:
http://www.engadget.com/2013/04/30/google-glass-review/
and don't see anything where I'd prefer Glass over a phone.
There was a lot of voice stuff, similar to Siri, and Google's implementation may be better, buy it's not clear to me where the heads up display adds a lot of value over voice response, or voice response plus looking at your phone.
The biggest drawback to me is the very limited, 2D controller paradigm. It sounded a lot like the kind of UIs you see for DVD players, where you mainly navigate through Left/Right (and occasionally Up/Down) buttons. Versus the touch screen paradigm of being able to select and manipulate objects directly.
To me, this leaves a very narrow range of use cases where something like Glass provides the optimal user experience. Something where you need a display, but it takes too long to take your phone from your pocket, where a two way navigation UI suffices, and having to reach up to your temple to control it is not too awkward. Or a voice UI, where something more than a voice response is needed (otherwise, phone plus Siri like capability plus audio headset would suffice).
I'm sure these applications exist. I don't think any of the applications described in the Engadget review fit the bill.
So, as a Glass tester, tell me what I am missing. What are you seeing as the big wins of using Glass over just using your phone?