My phone has a memo app, it's usually used for ideas for coursework, possible programming ideas and drunk thoughts. Some of them make sense later one, some don't. If I have a tricky bit of (CS) coursework I prefer to mull over it away from the computer. If I understand what the coursework requires and vaguely how the system works then it's not always necessary to always consult documentation - the gaps can be filled in when it comes to implementation. For example, I can think about some code that requires the computer to convert a string to an array of bytes but I don't need to know the name of the Java method that lets you do that, only that it's possible. Walking, taking showers, doing the washing up and preparing dinner are all great activities for thinking. It's just a shame that when I'm not doing any of those things my mind is probably occupied (mostly uselessly) reading or watching stuff on the Internet...
I'm not sure how I feel about Google Glass, but I have thought that since I often generate ideas when I'm doing physical, it would be nice to be able to record my ideas without having to stop and pull out my phone. Also, I think that taking something you're thinking about out of its typical context is usually a good way to get some perspective and make some connections that might be hard to see or imagine otherwise.
I don't think you really need a Google Glass style screen for that. Perhaps you could rig up a microphone (like those ones that TV presenters wear) and some earphones for feedback? It could be connected to an Android phone or something and start recording if you say "record" or "start memo". A hands-free dictaphone.