The next version of Microsoft Office for Mac will ditch its Entourage app -- the Mac's version of Outlook -- replacing it with what we've all wanted from the start: the actual Outlook, but for Mac.
The change will happen late next year when Office for Mac 2010 ships, with Microsoft promising updates that provide much tighter integration with OS X.
One update involves the database in which Outlook stores all your data. The 'soft say's it'll be a fast, file-based database, which means it'll work with Spotlight (OS X's built-in desktop-search system) and Time Machine (its system-wide backup client).
It's built using Cocoa. Not the dried seed, but the programming framework that OS X itself is built on. By using this, Microsoft can let Outlook's tentacles access and utilise deeper parts of OS X's core technologies itself. This can only be a good thing.
Note that the next version of OS X -- OS X Snow Leopard -- comes with native support for Microsoft Exchange. This means the OS's Mail app will buddy up to your work's Exchange server without you shelling out for Office in the first place.
You can read more details at the official Office for Mac blog.