The release is in active development and is currently strongly discouraged from using it in combat conditions - better try playing somewhere on the test site. To test WordPress 3.5, use WordPress Beta Tester . You can also download the beta version here .
What's new?
For the user:
Appearance: a simplified login screen, a new color picker, as well as an improved console with support for Retina displays
Plugins: Now you can browse the list and install the plugins you have marked as “Favorite” on WordPress.org directly from the console.
Mobile apps: it will now be much easier to link your WordPress blogs to your mobile devices, because XML-RPC is now enabled by default .
Links: when installing a fresh WordPress, the “Links” section will no longer exist, but there is a special plugin for this.
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For developer:
Updated external libraries: TinyMCE 3.5.6. SimplePie 1.3. jQuery 1.8.2. jQuery UI 1.9. Backbone 0.9.2 and Underscore 1.3.3 have also been added.
WP Query: you can request posts in the order specified in post__in .
XML-RPC: new user management, profile editing and post revisions. Also AtomPub has been removed.
Multisite:switch_to_blog() used more often, it has become faster and better. You can use Multisite mode by setting WP to a subdirectory. Downloaded files will no longer be stored in the ms-files directory (also for fresh installations only).
TinyMCE: The “Views” API has been added, with which the behavior of some elements can now be tracked in the visual editor.
Post API: global performance improvements when working with page hierarchies and “ancestors” posts.
Comments API: Search by comments with a certain status or using a meta-query (the same as WP_Query ).
oEmbed: support has been added for several oEmbed providers; HTTPS is also now working.
Bonus!
A full-fledged “combat” release of WordPress 3.5 is scheduled for December 5, 2012 . But Automattic decided to make a gift for its adherents, and has already released a new theme, Twenty Twelve , which will be the new default theme in WordPress in 2013. This is quite a nice, easy and completely responsive theme for WP. Download it here .