The image shown in this article does a good job of highlighting the usefulness of Glass. It's not just a heads up display. It's the smarts of knowing where you are, what you are doing, what you plan to do in order to provide relevant information in an automatic and unobtrusive way.
"Oh, I see you're at the airport and you have tickets on flight 644. Here's some useful departure info." Instead of finding a departure screen or tap-tap-tapping on your phone - it's just there.
I can see the contextual bit, but I'm not really sold—at least, not yet—on the HUD form-factor. Why can't I view the smartly-pulled-up, contextual information on a smartphone screen? There are a handful of situations where no-hands usage would be nice, but for the most part a screen works fine for me. There are lots of things I'd like improved about quick, non-frustrating access to information, but they're mostly the software/indexing/querying/"smarts", not the display technology.
"Oh, I see you're at the airport and you have tickets on flight 644. Here's some useful departure info." Instead of finding a departure screen or tap-tap-tapping on your phone - it's just there.
http://img.svbtle.com/dcurtis_24516029389500_raw.jpg