My feeling is that this effect might fade away as people become more used to the device. Anyone who wears glasses can tell you that the first time you put them on, the frames are very distracting in your peripheral vision. You become accustomed to them rapidly, however-- within days, the frames are invisible, and you retain this even when you take them off for a while.
A similar phenomenon takes place when driving. Every now and then you realize that you weren't watching the road at all, just driving along automatically with your peripheral vision. And the haptic compass experiments have demonstrated people have the ability to gain an unconscious sense of location from external stimulus.
Obviously something popping up in focus is always going to be distracting, but with a notification icon in the corner of your eye, it's entirely possible that one would grow used to it and stop consciously noticing its appearance-- you'd simply have a somewhat-unconscious "email sense".
And there's no reason that should distract one from what they're doing; when the mail comes to my door, I don't stop whatever I'm doing and go read it. I make a mental note to check the mail when I get a chance, and continue the conversation.
I'm pretty excited about this technology.