With Outlook 2007 Microsoft has made a significant investment in time and project management which is ably reflected in the "To-Do Bar" and the instant search capability. Additionally Outlook 2007 includes a built-in RSS aggregator so that you can subscribe to RSS feeds from your favorite sites or blogs.
Outlook 2007 does not make as extensive a use of the Ribbon interface that is found in (most of) the rest of the Office 2007 suite. The "Explorer View" (which is the view you use when you're viewing your Inbox list of e-mails, your Calendar, etc.) still uses essentially the same interface that Outlook 2003 used (with a few minor changes). The Ribbon shows up in Outlook in the "Inspector View" which is what you use when you actually open an e-mail item or an appointment item and work with that individual item.
Outlook 2007 no longer has its own editor - in fact Outlook 2007 uses the Word editor exclusively. Don't have Word? No problem, Outlook 2007 comes with a word.dll file that provides the editor functionality to Outlook even if Word isn't installed on the machine.