A very good point. When Marc Weiser said that technology will fade into the background, he probably wasn’t implying that it will fade into our bodies. Google Glass, in its current form, is not less intrusive or awkward to use than a smartphone. Neither for the user nor for the people around them.
Your body isn’t a tool for delivering your experience: it is your experience. Merging the body with a technological control surface doesn’t magically transform the act of manipulating that surface into bodily experience. I’m not a cyborg (yet) so I can’t be sure, but I suspect the effect is more the opposite: alienating you from the direct bodily experiences you already have by turning them into technological interfaces to be manipulated.