It's not due out until December, but WordPress 3.5 already has a beta release.
With the exception of a new theme, version 3.5 is primarily focused on removing and improving existing features, rather than adding new ones.
3.5 brings improvements to the media library, theme previews and plugin installer. It also removed the Links feature, which has been around for over a decade.
1) Links Have Gone
The Links feature was out-of-date. It had long been surpassed and improved on by the Menus in WordPress. So, version 3.5 will see the Links disappear entirely.
If you're on WordPress 3.4 and are using the Links feature it will remain for you. However, new WordPress installation will need to install this plugin to get the Links feature back.
2) Twenty Twelve Will be the Default Theme
Click here for our full write-up on the new Twenty Twelve theme. If you want to use it now, you can download Twenty Twelve from WordPress.org.
3) New Color Picker
With the new theme comes a small improvement in the live theme demos. There's a new, improved color picker:
4) Favorite Plugins
If you have plugins that you regularly install on all your WordPress sites, you can now favorite them on WordPress.org and find them easily via the Plugin Installer:
5) Media Improvements
The media library has been overhauled in 3.5. It is now easier and quicker to insert images into content. Click to insert an image and you'll see a large gallery inside a pop-up.
Click an image and a blue check and an "Insert" button will appear.
Click that "Insert" button and your task is complete:
Beta Tester Plugin
A quick piece of advice for those of you who want to test new, best versions of WordPress ... use the WordPress Beta Tester plugin. That will allow you to automatically install the very latest build of WordPress, directly from your admin area.
Of course, please don't use this on any site that you value highly.