There's an interesting (notice I didn't say fascinating, though 'tis) article here. At Mercer, we provide a laptop to each student as part of tuition, but we have no uniform policy on their use. Anyone who has watched a class being taught know students text, shop, and so on. I used to daydream and doodle; it's part of the human condition, I suppose, no matter the subject matter and law sometimes ain't exactly the series finale of Lost. (Which is probably a good thing, but I digress.)
But laptops are different, because of the impact of the screen on those behind it. I remember watching, for evaluation purposes, a professor from the back of the room and noticed a student playing solitaire, and when he won, 10 (or more) heads turned to watch the cards cascade as they magically do when you win. I even think laptops are poor note-taking devices, but that may be a generational thing -- may work for the young ones.
But what do you think of the approach of walking out of class, making the test harder, and so on for violations?