Wikipedia is "blacking out" the English version of it's site for 24 hours in protest for a bill that is being considered in Congress.
Essentially that means if you try to open an English wikipedia page, you will be greeted with a dark page containing some information about the issue. The wikipedia page actually seems to load for a fraction of second before getting the "black page", and if you hit stop fast enough you can access the content you want (tested in Chrome).
More info here:
http://abcnews.go.com/Technology/wireStory/wikipedia-black-wednesday-protest-15373309
Personally I grew a bit tired of Wikipedia's approach. Their big portrait banners were annoying enough... I find for such a site to block access to it's content for a whole day pretty shocking - keeping in mind that the bill is just being considered, and it highly likely to be rejected. All the content on Wikipedia is contributed by volunteers. I don't think there is much more to this site then this... therefore I think the founders should keep a low profile.
On the other side, it is commendable to raise concern about such an issue and not take risks and wait for too long - so part of the move is understandable and positive, in my opinion.