I'm tired tonight, but this is important.
If you don't know what the Stop Online Piracy Act (in the House of Representatives) is, or the Protect ID Act (in the Senate), read this article from the Stanford Law Review. I could explain it, and why it is such a horrendous idea, but Mark Lemley, David S. Levine, and David G. Post do such a great job -- so much better than I could (not surprising as they are professors of law) -- that it seems silly to reinvent the wheel.
[Edited to add: You can read Cory Doctorow's take on it here, here and here; and here is Mythbuster Adam Savage's opinion. I think the second link -- Cory Doctorow's column on what this will do to everyday Americans -- should be required reading for anyone who accesses the Internet or even owns a computer.]
After you've read it...
Contact your Representative and Senator. Time is short.