I just saw this when researching information on Google Glass. It looks unbelievably, undeniably, distracting. Hearing your directions is one thing, but having a simulated image of the directions constantly in front of you is another. Is google trying to kill people?
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi.bullfax.com%2Fimgs%2F4722cc01517cdd71ba7170fbace4448f0d863a5e.jpg&hash=63a22c1509d978b597572e8d4dde4352897c32c4)
http://www.cnn.com/2013/10/30/tech/mobile/google-glass-driving-ticket/
I'd say it's less distracting than constantly glancing over at a GPS. Certainly a lot less distracting than my habit of looking at road atlases while driving.
Now if Google Glass could show the line on the actual road and only on the actual road...