I believe the idea that these technologies is alienating is false. There are some people (such as myself) who simply do not wish to engage with their fellow passengers on a train or airplane. So, if someone politely speaks to me then I am forced to either a: engage with them (there's no harm in doing so, but I simply don't want to), or b: come up with some sort of way out of the conversation and hope to not appear rude (I don't wish to offend anyone, but I just don't want to talk to them). However, people are much less likely to speak to me if I'm wearing headphones or if I'm reading something on my phone, laptop, or tablet.
However, I also disagree here that Google Glass will stop being dorky, and I really think that it will be a while before it goes "mainstream." The reason is that people were somewhat hostile when the iPad was first released. Indeed, many people still look at tablet users as smug and see them as somehow offensive. So, as has been said here, now you're making the tablet very tiny, very expensive, and adding a nearly always-on camera to it.
Furthermore, I'd like to point out bluetooth ear pieces. You simply look like a smug bastard or an idiot when you're using one (full disclosure, I used to have one during college so that I could listen to music while riding my bike to class, but also keep an ear open for traffic etc.) And Google Glass is really not that much different from a bluetooth ear piece, except, again, that it's got a little screen and a nearly always-on camera.