No because anyone who already reads HN already knows SOPA. The only thing that will be effective is if sites that normal non-tech people visit go dark.
Despite the fact that the majority of HN readers already know about SOPA, I think it's an excellent idea for these other reasons.
It might also be an opportunity to get some of us off our butts and use the time we spend reading HN each day to call our representatives in congress instead.
So you think that HN being off for a few hours will make headlines in the worlds newspapers and on the main TV channels? Maybe as an "some tech websites were also offline [and nothing important was lost]" or maybe even (given the quality of some press) "other illegal hacking sites were down in protest against the bill".
I don't have a representative in congress but nonetheless expect congress is already pushing a similar law for my country.
I find the idea lacks any force as a demonstration.
Reddit, HackerNews & SlashDot down = Tech sites blackout
Reddit down = Remember that website that we reported was full of pedophiles last month? ...
Is more valuable than that.
To the eyes of history, you have symbolic value in participating of a protest.
People will talk about what you did or did not in historically important (game changer) times.
So is all about how do you want them to talk about you in relation to this?
I agree that HN we ought to be willing to go dark, (insofar as HN is a leader of anything) but still vote no on the grounds that it will be a meaningless gesture. Leaders should be willing to sacrifice as they ask from others, that doesn't mean it's helpful in every situation.
ps. I may be biased. I've never been very big on symbolic value.
Think it from different points of view.
For example: if HN goes down, it could be a fact noticeable for a journalist's investigation. With luck, it could become a paragraph in a New York Times article about this subject.
You can more influential than you are thinking.
For reference, all SOPA related articles on HN: http://www.hnsearch.com/search#request/all&q=SOPA
If you want to have real effect continue (or start) to write your congress-person, educate your friends, and pressure them into doing the same. Post on Facebook, twitter, etc.
Compared to these real actions, shutting down HN is useless pageantry.
Perhaps "going dark" can help encourage said companies to show support - in a similar way that the Reddit post has triggered this post.