I've seen a lot of people argue that sites like Hacker News shouldn't engage in a protest like this on the grounds that most of its audience probably already supports the protest's cause. I think this is a fundamentally flawed view about the nature of protesting.
It is without question that the most effective protests are those that have direct impacts on the opposition and its supporters, but protesting is bigger than that. It is about trying to be heard just as much as it is about being heard. It is about speaking your mind and standing behind things you believe in even when your protest may fall on deaf ears.
For that reason, the overwhelming amount of people within the Hacker News community that oppose SOPA is the perfect reason TO join in the protest.
I would miss Hacker News for the day, but I would take great pride in being a part of a community that stands up for what it believes in.