How much of the voice network goes across the internet now?
How many companies most if not all their business on the internet?
How much do the airlines depend on the internet? The ticketing counters have terminals that access some database housed in some data center. If you are traveling you could be stuck where ever you are at. Hell, how is all the flight information shared between the airports? I doubt that the FAA has a separate isolated network.
How much of the trading on the stock markets are done on the internet?
Go to the store and try to buy something with a credit or debit card. Your cards are verified across the internet.
Go to the bank and try to get your money out. Does the local branch of your bank have your account information? Or is that information stored in some data center that is accessed via the internet?
I could go on and on with examples. It is amazing how within the past 10 years the internet has become such an integral part of our daily lives. Just the other day, I tried to explain to my daughter that when I was growing up, most people had not even heard of the internet and you were lucking if your school had a computer. She just could not understand how we did things with out computers and access to the internet.
I would be interested in hearing from an economist on what the economic impact(both US & Global) would be if the internet was shut down for a day, a week, a month, etc.