Apparently there are some people on twitter who are confused and upset that Wikipedia (in English) has been blacked-out for the day.
If you haven't done so already, take a look at the announcements on Google, and Wikipedia. Follow the links for a more detailed explanation. Also, Wikipedia's pages on the bills in congress, SOPA (in the House) and PIPA (in the Senate) are not blocked.
Two other sites I'll recommend are this post at the Electronic Frontier Foundation, and this post at Mashable that breaks down the actual text of SOPA.
These bills are poorly written and will probably not even prevent the real sources of online piracy.