Not sure if this is true. FBI thinks this is needed to be done. A virus needs to be cleaned, and if you have the Virus after it is cleaned you can't get in the web if you have it. Just would require you to clean your computer to connect again.
Be prepared in case the articles and rumors turn out true.
My understanding is the net would not be shut down, but if you have the bug you will not be able to access the net because the government, unless they extend the deadline, will shut down a group of DNS numbers they have cleaned up and took over temporarily to keep the bug from spreading.
You think they would do that??? Heck, they would find a way to get on here and blame everyone else for their lack of protection from getting the virus and threaten to sue everyone and contact the FBI, CIA, FCC, FTC, BBB, Attorney Generals, the Army, Navy, M I C K E Y M O U S E .....
They still would not see the light of day!
Here's a fairly detailed article about this, from a reliable site: http://securitywatch.pcmag.com/malware/293327-will-your-browser-go-dark-on-march-8. It has a link to an Avira tool to work on your own system prior to March 8, thus avoiding any federally induced loss of connectivity. Here is that Avira link: http://techblog.avira.com/2012/01/23/avira-dns-repair-tool-released/en/.