After completing its yearly call for donations, Wikipedia is once more calling attention to itself by going offline for 24 hours but this time in the name of the ongoing legislation in the US that could damage the free and open Internet. The SOPA or Stop Online Piracy Act is seen by many as censorship which will alter the fundamental way the Internet works and has worked so far.
It will be interesting to see what their user's feedback on this move will be and if other websites and services of equal or greater importance will go into protest mode.
-Update: Some websites have already followed suit, namely Boing Boing, Wordpress, Reddit, Imgur, Mojang, Tucows and dozens of other are following suit.