As well as the security fix mentioned above, this version also fixes a few bugs, makes the blog signup process much faster and adds a new “Global Terms” Site Admin page.
The “Global Terms” page is one I should have added years ago. Currently it’s fairly bare, but hopefully in future versions of WordPress it will be expanded. It allows the Site Admin to “fix” the terms (tags and categories) used in MU blogs. These terms are normally synced with the “sitecategories” table but sometimes they go astray. This can happen if you “import” a blog using PHPMyAdmin without going through the WordPress importer, or if a plugin manipulates the terms table directly.
WordPress MU forces the “slug” used by terms to be a sanitized version of the “name”, which isn’t the case in WordPress. This page can optionally rename the terms so they match the slug. It doesn’t do the opposite because that would break public facing URLs on the site. (I must extend a big thank you to Deanna for helping debug that page)