The SOPA and PIPA acronyms stand for "Stop Online Piracy Act" and "PROTECT Intellectual Property Act" (with PROTECT a nifty little acronym for "Preventing Real Online Threats to Economic Creativity and Theft"). These sound fairly innocuous, I suppose, but Wikipedia and other opponents of the bills fear that their passage would fundamentally damage the structure of the Internet. So we had what we had yesterday: an unprecedented blackout/protest coordination among major Internet sites.
The sites' strategy seems to have worked, at least in the short term. By the end of the day yesterday, support for the bill in Congress had weakened. And today, though all is back to normal, people are still talking about these bills: by my informal tally, approximately 150 articles about SOPA/PIPA have been published in the past 3 hours. If Wikipedia and friends wanted to make waves, they appear to have succeeded, but are well aware of the well-connected opponents they face.
More about this:
"PROTECT IP / SOPA Breaks The Internet" (a video on Vimeo, by Fight for the Future)
"What are SOPA and PIPA? Education about the bills continues after online protests" (Washington Post blog)
"Put down the pitch forks on SOPA" by David Pogue (New York Times)
"SOPA will take us back to the dark ages" on Mashable
(This post was aided by research by Dominika Gergely '13.)