WordPress now has an upgraded Toolbar (previously known as the admin bar) and a new HTML5 media uploader that uses Plupload, an open source upload handler with drag-and-drop functionality. WordPress now supports RAR and 7z archive formats.

The responsive design usability of HTML5 has been implemented to help WordPress work on small-screen devices like the iPad and tablets. As you reduce the screen size, features such as the side menu automatically collapse.
Users will find a reduction in repetitive clicking with our new flyout submenus. As you hover over each main menu item in your dashboard navigation, the submenus will appear, providing single-click access to any dashboard tool.
For browsers without HTML5 support, it uses fallback methods, which includes Flash and HTML4. There are also improvements to the Metadata, Settings and Editor APIs, and a new tutorial for beginners has been added.
Overall performance of WordPress is improved.
However, one of the best changes is how quickly I can write a new post or enact a new action within the WordPress dashboard.
Another good feature is the tutorial pointers which appear the first time you see the changes in the dashboard. It’s useful for novice WordPress users.

I highly recommend upgrading or using WordPress today.