Actually, SOPA has nothing to do with the shutdown of Megaupload from what I've heard. I'm not completely sure since I haven't read about this yet, so if anyone knows correct me if I'm wrong.
Either they shut down Megaupload to prove that they CAN and will shut down anything with copyright infringement material on it when/if the bill passes, OR the founders decided to shut down their site by themselves. That's what I've seen people talking about, and since I don't know much about it myself, those two are the possibilities whereas one of them I think might be the reason.
Also, you know how much I love anime.. and the site I hang on have a lot of video mirrors in Megavideo, which of course have their source from Megaupload. From times to times there are some idiots who decides to watch anime, and some of them have no idea SOPA even exists and it's hilarious watching them rage in the chat because of that.
Most discussions about SOPA/PIPA actually start because of those idiots, so that's where I gain my knowledge from since I hang on the site practically every day, lol.