During the long march from Office 2003 to 2007, I heard the same thing over and over again: "I hate the ribbon!"
Power users of Office complained the most. Their fingers had been trained to work with menus, not ribbons. And the distribution of features seemed arbitrary: Were macros on the Insert ribbon, or was that the View ribbon? No wonder so many organizations had problems moving to Office 2007.
[ Also on InfoWorld.com: Top 10 Office 2010 features for business. | Save money on Office 2010 by first upgrading to Office 2007. | Why I hate Microsoft Office 2010. ]
The transition to Office 2010 promises to be a whole lot smoother. In part, that's because everybody has had their struggle with the Ribbon and has (begrudgingly) accepted it. In part, it's because Microsoft has actually improved the ribbon based on user feedback. My circle of Office friends tends to be pretty opinionated and, uh, entrenched -- but most of them are now saying that they'll move to Office 2010.
In Office 2007, the ribbons were more or less set in concrete: While you could change Office 2003's menus quickly and easily, Office 2007 locked 'em down. Now in Office 2010, you can suddenly change the ribbons: Customizing ribbons is as simple as right-clicking an empty part of the ribbon you wish to change and choosing Customize the Ribbon. Score one (albeit long overdue) for the Microsoft team.
The Office 2010 ribbon now appears everywhere. Outlook 2007 had menus, but when you started a new message, you suddenly flipped on the ribbon. Whiplash. Outlook 2010 also makes some worthwhile functions a little easier to find -- but more important, you don't have to switch back and forth between thinking in menu and thinking in ribbon.