Today Wikipedia is supposed to be "offline" with a blackout to support the protests against SOPA and PIPA. Buzzfeed already has a collection of angry students who can't do their homework due to the content being unavailable.
There's a catch.
I don't think this a weak protest. The type of people in favour of SOPA, for example, are unlikely to figure the 'hack' out.
It does raise a question; why are Wikipedia using this blackout tactic?
One answer is loud and clear to anyone with experience in search marketing. This approach should not impact Wikipedia's awesome SEO. There are no redirects here. No 404s, 503s or other server side rejections. Google can still index the full page of content.
Caution! This does not mean you can copy Wikipedia. Google is unlikely to let other sites away with this - it's not good form to have too a high percentage of a page's content accessible to spiders and not immediately visible to users. You risk falling into the 'hidden text' trap which has been part of Google's guidelines for years.