Here is one litany of complaints. Nicholas Carr speaks to the issue and he recommends this summary piece, to defend his view that the internet is in some regards making our thoughts less focused and more superficial.
I've read the piece and I don't yet see the evidence. There are plenty of studies where the experimenter imposes his or her own version of multitasking on the participants and then sees their performance fall.
I'm simply not convinced or even moved in my priors by these studies. I can't operate a German Waschmaschine (imposed on me), and that's without an internet connection running in the background. Nor would I do well if confronted by, say, the open internet windows of Brad DeLong, or his devices, whatever they may be, and in the broader scheme of things surely he counts as intellectually close to me. Yet overall my life runs quite smoothly.
To sound intentionally petulant, the only multitasking that works for me is mine, mine, mine! Until I see a study showing that self-chosen multi-tasking programs lower performance, I don't see that the needle has budged.
I do see stronger evidence (as cited) that video games make people more aggressive. I also see overwhelming evidence that the internet gets people to read and write more. The latter is probably a good thing. I also believe the internet leads to less interest in long novels and more interest in non-fiction. I won't judge that one, but it's misleading to cite only the decline of interest in long novels and by the way don't forget Harry Potter, the form is hardly dead.
I do, by the way, ban laptops in my smaller classes. But that's paternalism, and the desire to produce a class-level publc good, not fear of my students' cognitive decline. I can well imagine that they are processing more information, and doing it more effectively, when they are not listening to me, and the other students, so intently.
For extensions of my argument, see my book Create Your Own Economy, soon to be released in paperback with the new and superior title The Age of the Infovore.