Let me start off by saying that the interface rocks. Use it for awhile, then go back to an application that is structured around menus, and there is this giant feeling of “What have we been doing for all these years? The entire industry is stupid!”
The interface is that good.
But Office 2007’s downfall will be the same downfall that Office XP had, and the same massive problem that Open Office has:
Slow load times.
A common use for Word is to spell check random bits of text. Click the blue W, [cntrl-v], [f7].
Under Office 2007 that procedure is now Click the blue W, [Whistle show tunes], [take a short nap], [cntrl-v], [f7]
Once any of the Office 2007 applications get started up they perform well (though Outlook has some minor performance issues) and yes there are performance gains to be had once the code base is cleaned up and readied for release, but those minor speed gains are not likely to offset the overall slow load time for what users expect to be a very simple set of applications (Write text, add numbers together, send and recieve email).
It is important for developers to remember that ultimately the users do not care how eloquent our code base is, they just care if the software delivers the desired functionality. Does eloquent code enable rapid deployment of features that the users desire? Often times yes, but if a user can load up a web app in less time than it takes to load up an eloquently programmed desktop application, well, which one do you really expect the user to use?