I find both experiences unpleasant, although in different ways. Of course, it may all be enculturation, but the effect is real. When reading e-ink or lcd displays, after a time I just feel compelled to put it down and do something else. When reading a book, I often find that time has just gone, and the only reason to stop is that there is something else that needs doing.
I agree entirely that the convenience of having 6M books at hand and ready to go at a moments notice is phenomenal, and sometimes I succumb to that argument. For me, the medium then just kills reading for pleasure stone dead, and it becomes "read only if you must."