Giving our office's Glass to people to test, they're so distracted that they'll walk into things. Sometimes these things are pillars clearly visible at eye level.
I personally hate the idea of drivers wearing these things. My undergraduate was in psychology, neurophysiology, and hence I've been formally trained in attention and perception - I've got a better idea than layfolk on how these are compromised, though I'm not a professional in the field. In my opinion, the Glass is a significant attentional split - which is bad for driving. One example: say voice control is working fine (it doesn't always). You still have to take your eyes off the road, target a small reticle, make sure the glass is responding correctly. Even after that, there's still issues like just having a phone call in the car, which regardless of the device is a driving-performance-reducing attentional split.
Glass really, really impresses me as a technological feat; as a product I think it's a solution looking for a problem; and as a social phenomenon, I think it's quite dangerous when mixed with common activities like driving.