Shutting down facebook and twiiter is the most effective way of getting the message across. So many people I know have never heard of SOPA and don't care about it. If the issue was brought to facebook and twitter a LOT more people will start caring.
I really think the blackout protests are going to send the strongest message, if google, facebook, and twitter were to blackout or even just redirect to an anti-SOPA page for the 12-24 hours congress would back off quite a bit faster. Just because they are in a position of authority doesn't mean they can push through what they want, they are treading on thin ice and a large amount of people are waiting underneath for when it breaks.
"That's just silly. Closing a global business in reaction to single-issue national politics is foolish."
Should SOPA or anything like it pass Costolo, the first time someone posts "illegal content" on a twitter, your site will be closed for a lot longer than 24 hours and not by your choice. Your "global business" will be over.
Don't think for a second the government wouldn't love to make a forum for public discussion disappear. Twitter will be one of the first to go. They don't want you to discuss what you think, they want you to watch the news networks and be told what to think. Take an active role in fighting back or don't claim you're against it.