New user interface:
Blender 2.5 has a new GUI layout, with updated graphic design and a new icon set. The GUI layout has been re-designed to be clearer, better organised and easier to navigate, and is fully customisable with Python scripting. Other improvements include a new file browser, customisable tool shelf and more.
Customizable keyboard shortcuts
Blender 2.5 has been designed from scratch to enable users to configure their own keyboard shortcuts. Key definitions are be grouped in "key maps", and each map can be fully customized and saved. Keymaps can also be configured for special input methods such as directional gestures and tweak events, any-key modifiers, or multi-key input
Sculpt mode in Blender has been optimized, increasing drawing and editing performance significantly, and reducing memory usage to support more detailed models. New tools have been added and existing ones improved. Multiresolution meshes have also been rewritten, now available as a modifier to integrate better with the animation system, and preserving displacements when editing the mesh topology
Blender 2.56 is still under development but considered stable
Blender 2.56 current stage:
More to come...