WordPress 3.4 Beta 1 is out
WordPress developers have released the first beta of their next major update.
WordPress 3.4 Beta 1 is now available for download and testing.
Developers are suggesting not using this build on production sites.
This update seems to be focused on theming support enhancements:
Theme Customizer with Previewer
Flexible Custom Header Sizes
Selecting Custom Header and Background Images from Media Library
Better experience searching for and choosing a theme