It's funny, because from my perspective as a casual office user, I actually thought the menus made things a little easier to use, even if I needed to "re-learn" where things were.
My wife however, much more of a "power" office user, has completely sworn off of them. This is a person that knew pretty much where every menu item on word and excel was by memory. Her experience has been destroyed, so much that I needed to re-install 2003 on all the machines that she would use.
This is the engineering equivalent of offering discounts to new users, while ignoring loyal customers; it leads to churn, but not much progress for day to day users (i.e. the biggest users of the software). Applications that I like the most have "levels" of the user interface; you can switch to a more complete, complex, user interface once you get more used to the program.
It would seem that existing users' knowledge of menu/button layout was sacrificed for new users' organizational benefits.
From a "never having used Office before" point of view, it is more logical now. From my power user's point of view, the first 30 hours of usage had an additional 5-10 hours (wag) of "okay, where would they have moved THAT feature to?"
Exactly how I felt about the "new" Microsoft Office UI and the straw that broke the camels back on my continued use of that software.