For those of you uninformed this is a protest against the passage of SOPA and PIPA, two overly aggressive acts that target piracy sites but contain clauses that can also shut down pretty much any site whatsoever. Sites that rely on third parties (i.e. most social networks, YouTube, Mediafire, etc) will get shut down pretty much immediately and the acts give Congress the power to shut down any site they don't like.
Complaints to Congress about the act were received pretty much like this.
People: Hey this violates our freedom of speech.
Congress: Don't worry we're only targetting sites dedicated to piracy.
People: Then write that in the bill.
Congress: LOL don't worry we won't abuse our power we promise.
People: Why don't you write it in the bill then?
Congress: Because we know encroaching on your first amendment rights is wrong and we promise we won't do it, really. We promise.
PIPA was made as an "OKAY okay we know you don't like SOPA, here's a better act" but it still uses DNS blocking and other practices in SOPA and it's basically the same bill under a different name, so don't be fooled. Spread the word about them both.
I've drafted all of my posts to be invisible for the duration of the blackout and this site will be back up on the 19th of January.
Props to Wikipedia, Google, Ludum Dare, Equestria Daily (rofl), AndyGames, HackThisSite! and all the other sites/communities that set up protests; you guys rock. Going to try to keep a running list of blackouts.
EDIT: The MPAA made a statement. Interesting how they're still calling it an "anti-piracy" bill designed to "protect American jobs from foreign criminals" and not mention anything people are actually protesting against at all. Credits to a certain CaptainLepidus for showing me this.