At RSA Europe, Wikipedia founder Jimmy Wales said the site's blackout played a key part in defeating the USA's controversial Stop Online Piracy Act (SOPA).
The English version of Wikipedia, Reddit and hundreds of other smaller websites coordinated a notional service blackout for a day in mid-January to raise awareness of SOPA. Wales described SOPA as introducing a Chinese-style blocking system in response to complaints about copyright infringement. In response, Wales said, 10 million people contacted Congress (an unnamed senator told Wales) and the bill was pulled days later.
I am quite anti-piracy. This was a strike against bad legislation.