Wikimedia Bugzilla is closed!

I'd want the possibility to add a site wide notice rendered at the top of each
wiki page. Before rendering any page the wiki engine would check for the
existance of a page something like [[MediaWiki:Site notice]] and if it exists it
would render the contents of that page first. This would be good for informing
on site maintenance, feature upgrades or whatever that the site admins want
everyone to take notice on.

See http://meta.wikimedia.org/wiki/Site_notice for the same description and
maybe a discussion on the issue too.