PM is one of the major, well known software developer forums.
Sorry to blow your bubble, but Perlmonks is just space dust. It's unimportant in the global scale. Noone significant will have heard of Perlmonks, let alone be impressed by a blackout. Really, do you think there's an American senator or congress (wo)man who will say, "I was going to vote in favour of SOPA, but now that Perlmonks is blocked for 24 hours, I vote against it"?
Not that I expect Wikipedia going black will matter. That's as useful as wearing pink for a month in breast cancer awareness month, or sprouting facial hair in November in an effort to cure or prevent cancer or some other disease. Changing your life style or donating to research may though.
I've been saying this for 2 decades: if people keep violating copyrights, it will come back and bite you. SOPA doesn't surprise me -- that it has taken this long does. Sure, "our" community is now mighty upset about SOPA, but I seldomly hear anything constructive from the same community to prevent piracy. In fact, the community is full of people with hundreds of gigabytes of illegally downloaded music and movies. Fess up, how many of you have never downloaded a pirated copy of a movie, a piece of music, a book, or something else that should have been paid for?
[Cue the flock of people that will come with arguments that the entertainments industry business model is outdated: that's irrelevant. It's not your product, it's theirs, so they can use whatever business model they want. And then there are the people who claim "but if I really like it, I'll buy it". Yeah, sure.]
P.S. If Microsoft shutdowns Bing for 24 hours, will we give up open source?