If you want/need to view Wikipedia, you will face a problem, obviously, when the site goes down. However, using Google cache, you could very well side-step the blackout.
So let's say you're looking for... bagels on Wikipedia for some reason. On Google, all you have to do is search "Wikipedia" and whatever you wish to look up. So, enter "Wikipedia bagel" on Google.
To view the cached page, there are arrows on the side of the results. All you have to do is click/hover over the arrows, which will expand into a picture of a preview of the page. After this, just click "cached" and you'll be taken to the page that was cached by Google. Hopefully these pictures help (click on any/all the pictures for better resolution):
|Arrows on the side|