I'm not currently a user of Office 2007 but this video from Jensen Harris made me realize what the ribbon bar was and why they'd so radically changed the Office User Interface.
http://msstudios.vo.llnwd.net/o21/mix08/08_WMVs/UX09.wmv
This video shows how science is used to create something that's beautiful and useful.
Every User Interface Designer should view this.