The biggest feature in Microsoft's new Office 2007 suite is most certainly the interface. Gone are the menus and the toolbars -- now all the commands are available in the various tabs of the Ribbon. The Ribbon is much more intuitive -- but for seasoned users who have been working with Microsoft Office applications for more than a decade, it does involve a serious amount of unlearning.
An interesting add-in for Office applications like Word, PowerPoint, and Excel now brings back the menus and toolbars -- all inside a new Ribbon tab called "Menus"! The add-in is called Classic Menu Manager.