WordPress 3.5 Beta 1  has been released! The final version of WordPress 3.5 is expected to ship on 5th December 2012.
WordPress 3.5 will ship with a new default theme, named Twenty Twelve. But if you do not want to wait till December 2012, you can grab it now  at the WordPress Theme directory. It will work with WordPress 3.4.x as well
What’s New (General)
- Appearance: A simplified welcome screen. A new color picker. And the all-HiDPI (retina) dashboard.
- Accessibility: Keyboard navigation and screen reader support have both been improved.
- Plugins: You can browse and install plugins you’ve marked as favorites on WordPress.org, directly from your dashboard.
- Mobile: It’ll be easier to link up your WordPress install with our mobile apps , as XML-RPC is now enabled by default.
- Links: We’ve hidden the Link Manager for new installs. (Don’t worry, there’s a plugin for that .)
What’s New (For Developers)
- External libraries updated: TinyMCE 3.5.6. SimplePie 1.3. jQuery 1.8.2. jQuery UI 1.9 (and it’s not even released yet). We’ve also added Backbone 0.9.2 and Underscore 1.3.3, and you can use protocol-relative links when enqueueing scripts and styles. (#16560 )
- WP Query: You can now ask to receive posts in the order specified by
post__in. (#13729 )
- XML-RPC: New user management, profile editing, and post revision methods. We’ve also removed AtomPub. (#18428 , #21397 , #21866 )
- Multisite: switch_to_blog() is now used in more places, is faster, and more reliable. Also: You can now use multisite in a subdirectory, and uploaded files no longer go through ms-files (for new installs). (#21434 , #19796 , #19235 )
- TinyMCE: We’ve added API support for ‘views’; which you can use to offer previews and interaction of elements from the visual editor. (#21812 )
- Posts API: Major performance improvements when working with hierarchies of pages and post ancestors. Also, you can now ‘turn on’; native custom columns for taxonomies on edit post screens. (#11399 , #21309 , #21240 )
- Comments API: Search for comments of a particular status, or with a meta query (same as with WP_Query). (#21101 , #21003 )
- oEmbed: We’ve added support for a few oEmbed providers, and we now handle SSL links. (#15734 , #21635 , #16996 , #20102 )
Download: WordPress 3.5 Beta 1