This is one of the most thoroughly researched and tested facets of Office. I assure you that you're wrong on the discoverability of Office features for the average user: it went up by leaps and bounds with the ribbon, and in fact the entire ribbon was designed to address the fact that the most common feature requests for Office were for things that already existed.
Maybe the ribbon helps new Office users with discoverability, but for a power user like me, it gets in the way and slows me down. For instance, in order to change the font size of highlighted text in Word, I have to keep coming back to the Home tab, even if most of my current work involves a different tab (such as Page Layout or Review). Another way of viewing this is that the Ribbon forces me to work within and switch between certain modes (Insert, Page Layout, a general mode corresponding to the functions on the Home tab, etc.). These modes don't match my own working modes very well. With a toolbar/menu combination, I wasn't forced into these modes as much. Common processes, the ones currently placed in the Home tab, were always right there on the toolbar, and I didn't need to switch back and forth to use them.
In Word 2010 at least, a simple right-click on highlighted text brings up something like a mini Home tab. You can change the font, size, color, alignment and everything.
