I'm a UK citizen and am very concerned about SOPA. I'm also a member of the Avaaz organisation and signed their petition. You don't need to be a member to sign - it's here: http://www.avaaz.org/en/save_the_internet/?vl
Naturally, as a world-wide political organisation (with a small 'p') Avaaz are stressing the political implications of the bill, but the impact of legislation on writers, musicians, artists etc. is obvious and worrying. This is a way for non-US citizens to be involved. I have to say I find it horrifying that politicians in the US should feel entitled to affect internet users world-wide simply because they happen to host the big servers and companies. Let's let them know how we feel!