Professor Mark Lemley is quoted in the following article by Ameet Sachdev and Wailin Wong of the Chicago Tribune on the use of website blackouts to protest SOPA.

How do Internet companies stage a protest? By turning off their websites, of course.

Wikipedia, Boing Boing, Reddit and dozens of other lesser-known websites planned to go dark Wednesday in protest of proposed anti-piracy legislation in Congress that Internet companies maintain will encourage censorship of Web content and harm technological innovation.

The bills in Congress, pushed by Hollywood studios and other big media companies, target websites that let users download pirated movies, TV shows, music and other material in violation of U.S. copyright law. Most of these sites are outside of the United States, but the legislation would give the Justice Department and private companies tools to block them from American consumers.

...

"Sites like Wikipedia and Reddit going dark is a pretty dramatic step, and it will certainly raise awareness of the issue among a large Internet population that may not have been paying attention to SOPA," Stanford University law professor Mark Lemley said. "One of the reasons it is such a powerful statement is that it means lost traffic and, therefore, lost money for large commercial sites. That may be why sites like Twitter haven't signed on."