User-content websites such as YouTube would be greatly affected, and concern has been expressed that they may be shut down if the bill becomes law. Opponents state the legislation would enable law enforcement to remove an entire internet domain due to something posted on a single blog, arguing that an entire online community could be punished for the actions of a tiny minority. In a 1998 law, copyright owners are required to request the site to remove the infringing material within a certain amount of time. SOPA would bypass this "safe harbor" provision by placing the responsibility for detecting and policing infringement onto the site itself.
On Jan 24th, Congress will vote to pass internet censorship in the Senate, even though the vast majority of Americans are opposed. We need to kill the bill - PIPA in the Senate and SOPA in the House - to protect our rights to free speech, privacy, and prosperity.
See this timeline of SOPA and PIPA events and the activist backlash.