When we talk about reading, and whether The Screen is an enemy of The Book, we need to pause to make distinctions. We need to be aware that we read for several diffferent reasons: for pleasure, for benefits intellectual and academic (these are not always the same) and spiritual. We need to be aware that we read in different modes: the kind of intensely focused attentiveness that the medieval monastic world called studium, the kind of contemplative reflection that world called meditatio, the easy relaxation of reading for fun. We read different kinds of texts: sacred, artful, informative, pleasure-giving. And we read using different instruments: 
You can see from the above that it's just not helpful to talk about "the book" and "the screen." The books comes to us via multiple technologies, and there are many kinds of screen, which we interact with in a variety of ways. (Thus the distinctions made by Marshall McLuhan and many other thinkers since about the many and significant differences between watching TV and going to the movies.) You can also see that what makes the Kindle and other e-readers so productive of debates and arguments is their appearance under both "book" and "screen." They are a new way of experiencing books but also a new kind of screen.Distinguo!