Due to irreconcilable differences with Wikia, the WoWWiki community resolved in October 2010 that it would leave Wikia. However, it turned out that the domain name wowwiki.com had been legally transferred to Wikia upon WoWWiki joining the then-nascent network in 2007. As Wikia refused to relinquish control of the domain name to the previous owners, or consider selling the domain name (despite wanting admins to give up said domain name years earlier to move to wow.wikia.com), a mirror site was set up, and Curse offered to host it.
Wowpedia contains a complete copy of articles from WoWWiki as of 18 October 2010. If you choose to leave WoWWiki, any work you did on WoWWiki after that point may need to be redone on Wowpedia, although it's likely it has been updated by someone else.
There are a number of differences, some imperceptible to the lay user. The most obvious are that the sidebar is in its original place and it is not fixed width. Also, there were no ads on the wiki for the first 2 months of its creation, afterwards having just a single banner ad at the top of every page. Many of the new 'social' features introduced by Wikia do not exist, such as achievements and avatars. Additionally, your watchlist will remain private. (Most users are probably not even aware that watched pages are now 'followed' according to Wikia terminology, and are visible to the public.)
However, the content of the site is (currently) roughly the same, as is the community that runs it. It is intended to be the WoWWiki users wanted, not what was forced onto the community by corporate interference.
The decision among WoWWiki's administrators was practically unanimous, minus Kirkburn (who is a Wikia staff member). Virtually the entire active user base (as well as some new faces!) transferred to Wowpedia within a week of Wowpedia opening.
Some critics have noted that the new Wowpedia site has had trouble staying online at times. This is because the setup was rushed as they wanted to have it up in time for Wikia's forced switch to "Oasis" which was also just days before Blizzcon.
Reclaiming your user name
Wowpedia contains a tool to 'reclaim' one's user name. All you have to do is click on the 'Register' button and tell it your user name. The site will then generate a code; you can enter this code in an edit summary on your WoWWiki user page to confirm for the site that you are who you say you are. You will not lose any of the edits you made prior to 18 Octoboer 2010, as the entire history up to that point (including your user page and any subpages) is intact.
Note that, while you have the option of staying on WoWWiki, in under a week of wowpedia being live, practically the entire community (minus a few users here and there who hadn't heard yet) have moved to wowpedia. This means WoWWiki's information isn't getting updated for the 4.0.1 patch, while Wowpedia's is.