I think the biggest application for Glasses is hands-free, head-up, relatively inconspicuous outdoor on-foot turn-by-turn navigation. That is the nearest thing

I think the biggest application for Glasses is hands-free, head-up, relatively inconspicuous outdoor on-foot turn-by-turn navigation. That is the nearest thing you can get on-foot to the pleasure of in-car turn-by-turn navigation, with no need to walk around holding a mobile phone screen in front of your face. (The same kind of navigation indoors would be almost as wonderfully useful - especially for finding your way to the bloody airport departure gate! - but I assume that neither airport interiors nor v1 Google Glasses are ready to provide that today.) Combine that with the secondary application of convenient, hands-free, heads-up, relatively inconspicuous first-person photo and video recording and I think you have two pretty attractive and non-niche uses for Glasses to add to the long tail of more specialised applications. I'd say that the things most likely to hold back Glasses are price, privacy concerns (the wearer's and others'), possible social stigma, and fear of being mugged. (You could do a decent poor-man's approximation to Glasses' turn-by-turn navigation if you had a Bluetooth handset that did head tracking and the right software for your smartphone: you'd have the audio navigation directions in your ear, plus a turn-by-turn map display on the phone screen to glance at when you wanted to. I haven't heard of any such system though.)