Put __HIDDENCAT__ on the category page to hide that category from the list at the bottom of the article pages. This feature is intended to reduce the clutter from maintenance categories like [[Category:Articles with unsourced statements since December 2007]].
A feature to show the hidden categories for a page has been proposed, and is entirely possible in the backend, but the user inteface details have not been sorted out yet.
Red links now display text from [[MediaWiki:Red-link-title]] in their title attribute. By default, this is "(not yet written)" after the destination name. This feature is intended to inform casual readers of the nature of a red link.
Red links now point to action=editredlink instead of action=edit. The new action is more lenient in displaying edit permission errors, to avoid offending readers who are blocked and clicked a red link with no intention of editing.
Specifically, it redirects to the view page if the user doesn't have edit permissions, thus requiring the user to explicitly click the "edit" tab in order to see a block message.
The new parser is now live on all Wikimedia wikis.
The format of various MediaWiki namespace messages has been changed, to allow templates and parser functions in a much more intuitive way, similar to ordinary articles. Some local messages have hacks to work around bugs in the old parser, these hacks will need to be removed.
-- Tim Starling