Quoted from DemandProgress.org
What exactly does it do? The bill creates two blacklists of Internet domain names. The first can be added to by a court, the second by the Attorney General. Internet service providers (everyone from Comcast to PayPal to Google AdSense) would be required to block any domains on the first list. They would also receive immunity (and presumably the government's gratitude) for blocking domains on the second list.
-The list is for domains "dedicated to infringing activity," which is defined very broadly — any site where counterfeit goods or copyrighted material are "central to the activity of the Internet site" would be blocked.
-But it's just limited to copyright! How long do you think that will last? Once the Attorney General has a system set up for censoring the Internet, everyone who has a problem with a website will want to get in on it. How long before it's expanded to block Wikileaks, pornography, gambling, anarchists, supposed terrorists, and anybody else the Attorney General doesn't like that day? Do we want to live like the citizens of Iran and China?