If you're thinking about taking your website offline for a day or two (like today for SOPA/PIPA opposition, along with major websites like Wikipedia), please make sure you're doing it correctly so as to not hurt your SEO efforts. In a nutshell, the advice is to use a 503 HTTP status code to tell spiders that the website is temporary unavailable. Click here to read the full explanation.

For more information on these two pieces of legislation: http://www.pcworld.com/article/248298/sopa_and_pipa_just_the_facts.html