Folder Home Pages. You can enhance any folder with a view that summarizes the contents of subfolders with an Outlook Today-like Folder Summary Control, displays administrative messages and adds navigation controls. Extensive group policies. More deployment tools. Custom Installation Wizard and Office Profile Wizard to customize setup, choose components and set preferences.
ECF files are out.
COM is in. Enhanced Object Model. More objects, properties and events. Command Bars, Outlook Bar and synchronization are programmable. Outlook View Control.