If you've never used an Office application before and only need to access basic functions, then yes the Ribbon is a nice, simple interface.
However, if your looking for a rarely used feature and don't have the icon layouts memorized, it can be quite frustrating to use. Yes, the icon may be placed in a very logical place on one of the ribbon tabs, but that doesn't do me any good if it's a bizarre icon that I can't spot on first glance. Using a traditional menu, you can tap the first letter in the command your looking for to jump to it - for the Ribbon you have to randomly mouse-over every icon to see the tooltip before finding what you want. Further, at least with the old toolbar you could move icons around to locations that seem more natural to you, but the Ribbon offers no such customization (hiding a few icons doesn't count)
Note: I switched to a Mac at work last year (when IT is proud of an 8-minute boot time, switching becomes necessary to preserve sanity and while I prefer Linux, Mac has slightly better support for Enterprise applications), so I can't think of any specific examples offhand.
Unfortunately, I hear that an Office 2011 Mac upgrade is near at hand which brings the Ribbon interface to the Mac ... go LibreOffice (which does sometimes have better MS-backwards compatibility than MS)!