Most professors allow students to use laptops in class. Many students use them to take notes, to look at spreadsheets etc - but many students also use them for multi-tasking. And I use the term "multi-task" very broadly.
When I sit in other professor's classes to review teaching, I often am surprised by the amount of "multi-tasking" that is going on. I usually sit at the back where I can get a good view and invariably, students that are engaged in "multi-tasking" are on facebook, checking the weather, checking email etc. They aren't really multi-tasking, they are just doing a different task from what they are supposed to be doing.
That's why this article was particularly interesting to me. A Professor of New Media at NYU has basically banned laptops from class (except for specific projects). He's reporting a much improved environment.
A counter argument from a student might be:"Hey, if the prof says anything interesting or important, I'll pay attention", but I think this is perhaps a little delusional. I know that if I am at home watching a movie and in the quiet bit, I answer an email on my laptop, I invariably end up having to ask my wife: "what happened?" I am pretty sure that I can't multi-task effectively.