Offline wikipedia setup

An open source application automates the process of downloading and displaying all of Wikipedia on your desktop, a large task that takes more than a day to complete.

Dubbed Xowa, the software displays an offline copy of 4.4 million Wikipedia articles with full HTML formatting intact. You can even set up additional wikis, like Wiktionary or Wikquote, and navigate between them while offline. For example, you could "Click on 'Look up this word in Wiktionary' and instantly view the page in Wiktionary."-arstechnica source

Interesting article on setting up a local backup copy of wikipedia.