What effect is the blackout having, so far?
The purpose of the blackout is twofold: to raise awareness of SOPA and PIPA among the general public, and to encourage people to share their views with their representatives. It's too early to tell what the ultimate impact will be, but here are some early indicators, as of 1PM PT January 18:
More than 10,000 people have commented on the Wikimedia Foundation's blog post announcing the blackout. We have not done a content analysis, but at-a-glance it looks like the overwhelming majority support the blackout;
Almost immediately after the blackout launched, it became a trending topic on Twitter, globally, with hashtags including #factswithoutwikipedia, #SOPAstrike and #wikipediablackout. Trendistic says at one point, #wikipediablackout constituted 1% of all tweets, and Hotspots shows that SOPA has accounted for a quarter-million tweets hourly since the blackout began;
Google News contains 7,200 articles on the blackout;
More than 90 million people have seen the Wikipedia blackout page
More than five million people have looked up their elected representatives' contact information via the Wikipedia tool.