User interface and user experience are totally separate concepts. (Simon Guest; User Interface Blog.)
Microsoft did quite a bit of research in the raw usability of Office 2007, and found that while there is a learning curve for people like yourself, or me, who are experts in the tool, newer users and non-experts experienced much greater discoverability of more advanced features, and wound up using more of the application's features and power. Yes, there is a learning curve if you knew Office 2003 inside-out (which, frankly, few of us really did).
Now I'm not making apologies -- Microsoft's UIs haven't always been easy to use, and sometimes they fail miserably. (Personally I think not standardizing all of their office products on the Ribbon is a classic example -- there's a large context switch in my brain when I open Project or Visio, compared to when I open Word.)
As for what developers are "supposed" to do: Bear in mind that the ribbon isn't ideal for every scenario. If you're using it as a glorified, prettified toolbar, it's being used incorrectly. It's designed to help you organize literally hundreds (if not thousands) of commands in a way that makes them discoverable to your end user. It's supposed to reinforce the traditional experience of discovering the abilities of your application in a safe way (see any edition of About Face), when the depth of your application is too great to function within menus.
Aside from that, bear in mind that we should generally be making the most appropriate UI for our own audience, as Microsoft is attempting to do for its own audience. Again, we may find these things more difficult to use, as we are used to doing things a set way -- but it's the right thing (typically) for Microsoft to do. Remember that we programmers are not the target users of most UI. (How many of us turn off visual themes, for example? Now how many normal end users? BTW, I don't fall in that camp; I'm one of the few who actually finds Vista moderately attractive.)
Again, at the end of the day, what Microsoft does matters only to the extent that it becomes what your users expect, and then only if you can't educate them that "your way" is better. In any event, if usability is truly critical for you and your users, it's time to invest in usability testing and ensure that your application really is as usable as you think it is. And start reading usability sites. (You don't have to agree with them all, but understand them.) Here are some samples: