If you load such a file in Office 2007

One of the questions people ask about the new user interface is "how much training is required to get up to speed?"
Well, our design goal was to require no training at all. From the earliest prototypes, we were trying to design an experience so that people could sit down in front of Office 2007 and be effective right away at getting their work done. One of the reasons we didn't go more radical on the overall design was that we wanted to make the product comfortable to use--after all, at the end of the day, it's still Microsoft Office.
Jensen's job, of course, is to promote Office 2007. What he says may be true for those who have never used Microsoft Office, but he left out a few things.
Those who will have the most difficulty adapting are the great masses of office workers who have learned how to perform a dozen or so common tasks in Excel or Word, and they do them day after day. These people, for the most part, will experience serious frustration. In many cases, these workers don't even look at the "big picture." Rather, their task is broken down into a series of very specific steps that they've learned over the years. What happens when those steps no longer work?
Another potential source of frustration is the "deprecated features." Anyone who has followed the betas of Office 2007 know that quite a few features have been removed. Other features seem to be missing, but they are still available if you take some additional steps and them to your Quick Access Toolbar. The typical user won't know this.
Another problem. There are millions of customized Office apps in use that use toolbars and/or custom menus. If you load such a file in Office 2007, your familiar menu modifications and toolbars do not appear. Well, they are still there, but the user must know to click the Add-Ins tab. Then, all of the toolbars and menu modifications are visible, stuffed into a single unorganized chunk. Toolbars are no longer free-floating, and you may need to do some serious scrolling to even find the toolbar button you're looking for. And once a toolbar is displayed, there's no way to hide it.
I may be wrong, but I think it's unlikely that many large companies are going to perform massive upgrades to Office 2007. Those that do will require training, regardless of what Microsoft says.
Are the new Office 2007 features worth the effort and frustration? For some, yes. For most, no.