Minecraft wiki entry for Development_versions, associated text: Options
Added a 'hide' button to the chat screen
Performance
Improved multiplayer bandwidth usage
Improved client/server communication
Improved disconnection messages
Now includes the reason of the kick/ban.[1]
Improved text rendering
Improved world loading
Faster torch placing (less lag)
Added shovels in creative mode
Added server-side checks on games
Non-fancy render mode now works properly
Updated inventory icon from a Brick block to a chest
Limited player names to PC allowed names
Changed texture for mob spawners