Google has done this in an effort to help spread the word against the Protect IP Act (PIPA) in the Senate and the Stop Online Piracy Act (SOPA) in the House. Google does state:
“Fighting online piracy is important. The most effective way to shut down pirate websites is through targeted legislation that cuts off their funding. There’s no need to make American social networks, blogs and search engines censor the Internet or undermine the existing laws that have enabled the Web to thrive, creating millions of U.S. jobs.”
Both SOPA and PIPA are pushing the boundaries of who and how the internet should be controlled. China is an example of a country that already has restrictions and government censorship acts like the ones proposed in PIPA and SOPA. Google has provided a resource of materials on the subject which can be found on their More about SOPA and PIPA page.
Google is not the only website protesting today, many other major companies are participating in the protest as well. Wikipedia (English) has actual blocked the whole website in protest and (as seen below) gives users a feature to enter their zip code and find out who to contact to protest SOPA and PIPA. Google has generated a page where you can view a list of those opposing the acts.
The list goes on but we just wanted to make sure you got the picture. Interesting time we live in.