Wikipedia is going offline for 24 hours in 3 hours. Craigslist is going offline, I think already. Reddit is going offline as well... And those are just the big ones I've heard about. Nerdcore musician MC Frontalot's webpage is going offline too. Well, they'll just be plain pages explaining SOPA to those who've been living under a rock, giving links about it and advising you contact a representative.
Here's what wikipedia has to say:
Wikipedia:SOPA initiative/Take action - Wikipedia, the free encyclopedia
tl;dr They know it probably won't pass. They know it's been tables for now. But it's still a looming threat on the horizon. Something like that.