Pierre Far – Google+ – Website outages and blackouts the right way.
There is a lot of activity surrounding SOPA and PIPA, much of which speaks about an Internet-wide blackout in protest.
Many of these solutions involve altering what normally powers your CMS to instead display a message regarding the blackout and what you can do to help the cause. Depending on the site you plan on blacking out, it may be important to think long term and be a bit more explicit with your blackout policy.