If passed, this law would allow an entire internet domain to be shut down because of something one blog posted. In effect, punishing the whole for the actions of a few (or even one). Linking to a site deemed "offending" could cause a site to be shut down. A "copyrighted" song that happens to be playing in the background of posted video could get a site shut down, or at the very least, the video removed. And this bill would only affect American consumers. The United States has no legal jurisdiction over foreign countries.
So on January 18, 2012, there was a huge online protest that included sites like Wikepedia and Google and thousands and thousands of others (see the numbers here). Petitions were signed, emails were sent and sites were "blacked out." The end result--Congress has dropped SOPA to reevaluate. However, I'm sure we haven't heard the last of this.