I ban laptops in the college classes I teach, in physics.
For me the turning point was sitting in the back row of a large lecture taught by a colleague and seeing dozens of laptops open, and students reading CNN, Facebook, Travelocity, Gmail but none actually taking notes. Even if it was not distracting for the students themselves, it has to be distracting those around and behind them.
I offer an exemption for anyone who uses a laptop for notetaking. And in this case the student was kind enough to give me a copy at the end of the semester. So far I guess I have had around 500 student-classes, and precisely one exemption has been requested (and granted) -- and that was in a small class with a dozen students where cyberloafing is typically much less of a problem.
The policy is in my syllabus, and announced on Day One.