On the Tuesday 24th January 2012, the US Senate will vote on the internet censorship bill.
Whilst it is an American law, it has far reaching repurcusions for the web as a whole. Sites such as Reddit have said that on January 18th they are going to go dark between 8am and 8pm.
This plugin will let you join the cause. On 18th January your site will display a customisable page.
Search engine rankings will not be affected as the plugin sends a 503 status.
This plugin is available for download to be used on your WordPress self-hosted installation.