Q:

Is Microsoft's Ribbon UI really that great, from a usability perspective?

The first time I ever used it was at my current job. Among my co-workers, the feelings towards it for usability are mixed.
The other developer doesn't really care one way or the other, as long as the office does everything he needs it to do when writing reports.
The top manager likes it because it feels natural, and I feel the same way. But another co-worker finds it clunky and hard to use, although she admits that she only uses it at home as her machine hasn't been upgraded yet and that might change if she uses it more often at work.

Is the Ribbon UI really that innovative? 
What qualities about it make it a good or bad user interface mechanism?

Possibly related to: Adoption of the Ribbon UI

A:

One of the main drivers behind the Ribbon was discoverability of new functions. This was driven by research conducted by Microsoft that indicated that a large number of most requested features for Word actually already existed in the product; the user simply didn't know where to find it.
So the big, bold nature of the Ribbon actually lends itself to a browsing for features - far more so than menus, anyway. Keyboard shortcuts still exist for the Word/Excel ninjas, anyway ;)

A:

If you want the definitive answer then read Jensen Harris' blog entries (the office UI lead) which takes you right from the problems to the inception and development of the solution in the form of the ribbon.
It's a truly fascinating read, but you'll need to set aside literally a full day to get through all the posts.

A:

There are three groups of Office users:

Casual, or Know-nothing Users. This is your mom trying to type a recipe in Word, or your dad trying to make a list in Excel. These are the people who have no idea how to format tabs, they just hit the spacebar until the cursor is in about the right place. For these people, the Ribbon UI is a godsend, since they don't know what they're doing really. It makes it easier. They weren't used to the old style, so they don't care that it's gone. 
Hardcore Users. These people are fine because any seriously hardcore Office user uses keyboard shortcuts for everything. None of the keyboard shortcuts changed, so these people are unaffected by the upgrade. They might actually gain something, since anything they didn't know the shortcut to, they now have an incentive to learn.
Middle Users. People who use Office for various tasks, more than a Casual user, but not as much as a Hardcore user. This includes most programmers. They know just enough to be dangerous, but not enough to be proficient. The Ribbon UI annoys them most of all, just because it's different. But they'll get used to it, get over it, and probably learn more stuff about Office and how to use it as a result. The most important part is that none of them will feel strongly about it to change to something else. 

So, the one group that doesn't like it won't change and the other two are fine with it. This is why the uptake on Office 2007 is 2X the uptake of Office 2003, which was more or less Office 2000 with an updated UI.

