Did you notice that Wikipedia wasn’t working today?
Here’s why: they’re protesting a pair of bills before Congress, called SOPA and PIPA. The bills are supposed to combat internet piracy, but many people believe that they will destroy the freedom of the internet by allowing the government to block any site that hosts pirated material. That means, for instance, that because one person posts a pirated movie clip on YouTube, all of YouTube could be blocked.
This page does an entertaining (if biased) job of telling you why you should care, and providing some links to inform yourself about the issues.