Blacking out completely is too extreme. I would say a better approach is to put a full-page interstitial ad up over all of these sites with phone numbers to call, and a 30 second timer before you can use the service - be it Google, Facebook, Twitter, Reddit, HN, all the things. Let users get to the service but only after 30 seconds of looking at the phone numbers of US representatives offices, and a message that if SOPA passes, these sites will be gone for good.