We're going to be upgrading the software on the live site to the current development version, over the next 24 hours or so. However, we won't be releasing a tarball just yet. Before we do that, we want to obtain translations for the new interface text, and also to fix a few user-friendliness issues with the installer. We'll probably upgrade the smaller wikis first, and do the English Wikipedia fairly late in the peace. There might be short periods of downtime during this process.

A list of new features is at http://meta.wikipedia.org/wiki/MediaWiki_roadmap

-- Tim Starling