I don't have a problem with students using laptops in my classes, as a laptop is obvious and I can easily check that it is being used for legitimate purposes (creating notes, logging data from experiments) and not social netshirking. What causes more problems is students surreptitiously using smart phones to SMS each other or browse facebook. This usually goes on with them holding the phone below a desk out of sight so that it looks like they are fiddling with themselves when they should be working on Physics problems. Also, getting people to shut down a laptop is easy while ensuring that a phone is actually switched off is difficult. If it was up to me I'd deploy some technique to block the GSM frequencies while teaching, but that's probably against the law.
