Based on life experience, and more specifically my own experience with the internet, I opine that Mr. Carr's theory is rendered moot by the fact the interruption of concentration has taken many diverse forms throughout history. It is an individual choice to become self-disciplined in order to stay focused on that which is beneficial, which has been neglected by the majority in every sector of society. In my own use of the computer, I have gained access to a far greater amount of information in my areas of interest -- without otherwise having to spend a fortune on books. Almost all the "bonus" reading material I find I need in order to increase my knowledge was free to copy/download.
Here on the internet as well, I've found a way to relax and de-stress from a severe illness that prevents me from holding up a book to read, which I used to use as a form of stress relief: I can now watch t.v. shows and movies (also free) since I don't own a television.
The irony here is that this discussion was interrupted by commercials!