When I was in highschool, a bill was passed in congress called the "Communications Decency Act". I don't remember all the details, but basically it required ISPs and websites to block "indecent" material from minors on the internet. Eventually the bill was deemed unconstitutional by the Supreme Court.
Before it the bill was defeated, the Electronic Frontier Foundation (EFF) organized a blue ribbon campaign, asking people to post a picture of a blue ribbon and to "darken" websites in protest. (Darken here meant just making the background of your website black instead of white.) I remember virtually every major player in the internet participated in this protest. I remember atleast Yahoo and Netscape.com did, and they were probably the two most visited websites in the US at the time.
While the blackout protest by Reddit and Wikipedia is on the extreme end, I would have expected most major players to protest SOPA/PIPA in a similar small way. For example, Google's protest with their black-box doodle was tasteful and simple. (It is interesting that Google only did this on Google.com. They chose not to do this on Youtube.) Yahoo, Bing, Facebook, Ebay, Twitter, etc. could have done something very similar.
It got me thinking. Could it be the internet has changed so much, it's just hard to do something like this nowadays? Fifteen years ago a simple HTML color change was all that was necessary to change Yahoo's homepage. But nowadays, it might take a huge engineering undertaking. You have to make sure the change will appear correct on gajillions of browsers and mobile devices. Perhaps Google was able to protest only b/c they had a "doodle-change" option already engineered in place?