WordPress Version 3.3, named for Sonny Stitts, released to the public.
The most important change in my humble opinion is that they finally ditched the 4 different options for uploading media. Now- with easier uploading file type detection – A single upload button allows Drag-and-Drop media uploads, and the media autosorts on the type of file- .mov is a video etc.
They’ve reworked the dashboard design with a new toolbar in the dashboard, combining the Admin Bar and admin header giving you quick access to the most important functions and the new flyout menus, providing single-click access to any screen without scrolling through long lists of options on your left side admin menu.
The new user experience options provide new feature pointers, helping users navigate new features and also help direct new users to basic functions that they need through the dashboard welcome area.
New iPad/Tablet support is included in the admin area, but I’ve not had a chance to look into it yet.
via Version 3.3 « WordPress Codex.
As always with new versions, make a complete backup of your installation before upgrading and be careful with custom themes.