Here's what Wikipedia says about the strike and protest it worked so hard to organize.
Bottom line: 162 million people visited the blacked out site. Normally over 4 million visit the home page but, on the black out day, over 17 million, did a pretty impressive consciousness-raising effort. Even better, 4 million used the excellent tool provided on the blacked-out site, clicking through for information about which Congressperson to contact and how. Google recorded over 4.5 million signatures on the Stop SOPA petition, and the Electronic Frontier Foundation reported more than 1 million email messages were sent to Congress during the black out. On Jan 18, 6 Senators previously in support of the bill announced that they will withdraw their support for the bill.
Here's the full story, from Wikipedia, as of 8 am Jan 19. Click through for updates, of course:
"ENGLISH WIKIPEDIA BLACKOUT: http://en.wikipedia.org/wiki/English_Wikipedia_blackout
The English Wikipedia blackout occurred for 24 hours on January 18–19, 2012. In place of articles, the site showed only a message opposing the Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA), legislation being proposed in the United States Congress.
On January 16, the blackout was announced by Wikimedia founder Jimmy Wales and Wikimedia Foundation Executive Director Sue Gardner after conducting a 72-hour poll of the editing community. The general poll followed several weeks of discussion in smaller Wikipedia forums. The date was chosen to coincide with similar action by other websites, such as Reddit, and ran for 24 hours starting at 05:00 UTC (12 a.m. Eastern Standard Time) on January 18.
The Stop Online Piracy Act (SOPA) and the PROTECT IP Act (PIPA) are bills that were introduced into the United States House of Representatives and the United States Senate in the last quarter of 2011. The two bills, though different means, are designed to provide legal mechanisms for copyright holders, such as music and movie studios, to combat digital piracy that occurs on non-United States websites. Both bills are extensions of the earlier Digital Millennium Copyright Act (DMCA) that enabled content producers to issue "take down" notices to Internet Service Providers (ISPs) and websites to remove infringing content. While the DMCA has been considered effective for patrolling of websites within the United States, the DMCA fails to address infringement from foreign websites. Part of the language of the bills when originally proposed would allow for copyright owners to issue complaints to ISPs and other major websites, like Google or Bing, requiring them to remove the hostnames of infringing sites from their Domain name registry (DNS) and to delist entries in search engines to these sites.
Many of the companies and organizations supporting the proposed legislation are content producers, such as the Motion Picture Association of America, the Recording Industry Association of America and the Entertainment Software Association, and identified the need to have such laws to combat revenue losses associated with the copyright infringement from these foreign websites. However, some lawmakers and many technology and Internet firms and associations have expressed concerns that two bills' languages are too broad, and the concept of domain name blocking and search engine removal would amount to censorship of the Internet. A common criticism of the bill addresses broad and unclear language, such as what entails "deliberate actions to avoid confirming a high probability" for a website. Google's policy director, Bob Boorstin, stated that a site like YouTube supporting user-generated content "would just go dark immediately" to comply with the legislation.
In December 2011, SOPA was brought to the U.S. House Judiciary Committee to begin the process of marking up the bill prior to introduction to the House floor. During this time, numerous websites began displaying banners and messages promoting their readerships to contact Congress to stop the progress of the bill, stating that their sites would be "blacked out" should the bill pass as a law. The markup session, in which several proposed amendments to address the concerns of technology companies were defeated, was eventually put on hold prior to the end of the year, to be restarted once Congress came back in session. Several technology websites began proposing the idea of an "Internet blackout" on the same day to protest SOPA and PIPA to occur before SOPA would be voted on on the House floor as a means of further protest. Reddit was the first major site to announce an "Internet blackout" on 18 January 2012, and several other sites shortly followed, coordinating actions on that day. Though Senator Patrick Leahy, the main sponsor for SOPA, had stated that they would remove the controversial DNS provisions prior to the blackout date, sites continued to plan to continue with the demonstration.
In January 2012, in response to concerns over PIPA and SOPA, the White House stated that it "will not support legislation that reduces freedom of expression, increases cybersecurity risk, or undermines the dynamic, innovative global internet."
English Wikipedia's response
In line with the initial voices to stage an Internet blackout in December 2011, Wikipedia founder Jimmy Wales called for a "public uprising" against the proposed legislation, which critics fear would threaten free speech.
Wikimedia Executive Director Sue Gardner posted an announcement of the Foundation's support for the blackout proposal on Wikimedia's blog. The post received over 7000 responses from the general public within the first 24 hours of its posting.
Despite the majority support of those polled for the action, some Wikipedia editors blacked out their own user profile pages or resigned their administrative positions in protest of the protest; one veteran editor stated his "main concern is that it puts the organization in the role of advocacy, and that's a slippery slope".
Coordination of the 18 January action
Although there were no plans to block any mobile version of Wikipedia, German Wikipedia, Portuguese Wikipedia, Russian Wikipedia, Bulgarian Wikipedia, Ukrainian Wikipedia, Vietnamese Wikipedia and Wikimedia Commons were expected to run banners on 18 January, without a full blackout. Other sites indicating an intention to run banners included Google and TV Tropes, while websites planning a full blackout of at least several hours duration included Craigslist, Reddit, Boing Boing, A Softer World, Cake Wrecks, Destructoid, dotSUB, Free Press, Good.is, Good Old Games, little-apps.org, Mojang, MoveOn.org, Mozilla, Tucows CallAvoiders.com and TwitPic, as well as a number of other sites.
The announcement of the blackout was reported worldwide. Media that covered the story included ABC Australia, CBC, BBC, der Spiegel, Le Figaro, Le Monde, Fox News, The Guardian, Menafn, News Limited, Sky News, The Age, The Hindu, The New York Times, The Washington Post, The Wall Street Journal and The Times of India. 
Several media organizations including The Washington Post, The Guardian, and NPR encouraged a "crowdsourcing solution for those left searching for answers" during the Wikipedia blackout by inviting users to ask questions on Twitter using the hashtag #altwiki.
A Motion Picture Association of America (MPAA) executive dubbed the blackout plan an example of the "gimmicks and distortion" that inflamed passions while failing to solve the problem of copyright infringement by "draw[ing] people away from trying to resolve what is a real problem, which is that foreigners continue to steal the hard work of Americans". Former U.S. Senator and MPAA Director Chris Dodd stated that the coordinated shutdown was "also an abuse of power given the freedoms these companies enjoy in the marketplace today."
Dick Costolo, CEO of social networking site Twitter, rejected calls for Twitter to join the protest saying "[c]losing a global business in reaction to single-issue national politics is foolish." He later clarified he was referring to a blackout of Twitter and is supportive of the Wikipedia blackout.
The sponsor of the bill, Representative Lamar S. Smith, called the blackout a "publicity stunt," stating "it is ironic a website dedicated to providing information is spreading misinformation about the Stop Online Piracy Act."
During the blackout
The Wikimedia Foundation reported that over 162 million people had visited the blacked-out version of Wikipedia during the 24-hour period, at least 4 million of whom used the site's front page to look up contact information for their U.S. Congressional representatives. The usage of Wikipedia's front page increased enormously during the blackout with 17,535,733 page views recorded, compared with 4,873,388 on the previous day. A petition created and linked to by Google recorded over 4.5 million signatures, while the Electronic Frontier Foundation reported that more than 1 million email messages were sent to congressmen through their site during the blackout.
During the day of 18 January, six senators who had been sponsors of the bills, including Marco Rubio, PIPA's co-sponsor, Orrin Hatch, Kelly Ayotte, Roy Blunt, John Boozman, and Mark Kirk, stated that they would withdraw their support for the bills. Several other congressmen issued statements critical of the current versions of both bills.
The impact of the coordinated action was generally considered significant. Yochai Benkler of the Berkman Center for Internet & Society stated that the 18 January blackout was "a very strong public demonstration to suggest that what historically was seen as a technical system of rules that only influences the content industry has become something more," further adding "You've got millions of citizens who care enough to act. That's not trivial." California House member Darrell Issa called the collective effort an unprecedented means for upsetting a backroom lobbying effort. One Silicon Valley lobbyist said the content industry had "a lot to learn," noting that they don't have grassroots support: "There are no Facebook pages to call your congressman to support PIPA and SOPA."
Newspaper editorials had mixed views. The Boston Herald called the protest a "hissy fit" by "Internet powerhouses" saying, "within hours of the online protest, political supporters of the bill... began dropping like flies, thus proving how very powerful these cyber-bullies can be." The New York Times described the protest as "Noted, but as a Brief Inconvenience".  BBC News technology writer Rory Cellan-Jones was of the opinion that the blackout achieved its objectives but possibly at some cost to Wikipedia's reputation. The shutdown also prompted a cartoon response from Matt (Matthew Pritchett) in the British Daily Telegraph. "