I wanted to add one more comment because the SOPA is about removing safe harbor provisions affecting two different things, intellectual property AND defamation and libel. The first doesn't apply to those of you who don't produce intellectual property, but the second does apply to all of us.
As it stands now, if someone starts a Twitter/Facebook/YouTube campaign to damage your business, or simply sling mud about you, and does so anonymously, you have absolutely no recourse under the safe harbor provisions. You can't find the mudslinger, those companies won't tell you who it is anyway, even if they know, and those companies have NO obligation to address the issue. You can scream all you want. Too bad, so sad, while at the same time, those companies plaster ads all over the defamatory material and make money from it all.
Can it happen to you? Maybe. But I will tell you that I've been threatened publicly by several people impersonating lawyers, had a Twitter account created to impersonate me, and I'm hardly a public figure, and, over my long tenure on the net, faced a few attempts to damage my book sales.... I look at that stuff as part of what I do on the Internet, but it DOES happen. I'm just a regular, if somewhat loud, guy trying to make a basic living doing what I love to do.