I applaud the sites that have blacked out and/or put up anti-SOPA messages. SOPA and PIPA are bad news, and the word needs to be spread.
That said, there are 2 very important differences between those actions and the hypothetical LW blackout:
1) The sites that are blacking out are by and large sites that could be directly and severely hurt by the legislation. This is why I consider it okay for Wikipedia to black out about SOPA, but would be furious if the site were to black out because the editors didn't like some piece of immigration reform. They're not simply choosing to use their status as a soapbox, they actually must defeat these bills if they wish to continue existing.
2) The community driven sites that blacked out (including Reddit and Wikipedia) did so only after a serious discussion with their userbase. LW falls into this category, but no such discussion has taken place. Community site = community decision.
So IMO, a LW blackout would be an arbitrary political stance on a non-particularly-related issue, and a total snub to the community since we weren't consulted about it. I wouldn't be too pissed, since SOPA really does need to be stopped, but I would definitely consider it tacky.
You made the points I wished to better than I would have.
Another difference between LW and somewhere like reddit or wikipedia is they both have a large ratio of 'lurkers' to contributors, so there is a large number of users finding out about SOPA/PIPA for the first time today. Whereas my impression of lesswrong is that far more of the content is viewed by the same people who contribute content, so there isn't a silent mass of people who aren't aware of whats going on, as discussion isn't taking place in a less obvious subreddit or moderators section.
Our sister site apparently is:
Interesting, my model of Robin Hanson had him say something about the blackout and how it shows people are hypocrites. Though obviously he has strong opinions on intellectual property. I think it would have been a good idea to Blackout LessWrong today. It would have given us a status boost in most of the communities we frequent.