What is this internet Kill switch business. How could it possibly work in the US?

Good question. I was wondering the same thing. If they managed to shut down all the ISPs in the US at the flip of a switch, what's to stop someone from dialing up an ISP in Canada or Mexico or any foreign jurisdiction?

IIRC, they would shut down DNS, so you would still have internet access but your computer would not be able to get to any web pages, if that makes sense.

http://en.wikipedia.org/wiki/Domain_Name_System

more

http://en.wikipedia.org/wiki/ICANN