Windows A to Z has posted a review of the newly released Beta 1 build of Office 12.  Office is a big money maker for Microsoft so they are doing everything in their power to make sure that this version gives consumers and corportations enough incentive to upgrade:

Some of the new features to Office 12 include XML-based file formats (there is an "x" added to every Office file format now), a "ribbon" at the top replacing tradition drop-down menus and improved workflow between Office applications. Without a doubt, the most apparent change to Office is the ribbon-style menu at the top of most Office 12 programs. The old drop-down menus that included File, Edit, View and so on are gone from Office 12 and they are not even available as an interface option if you wanted them. At first we were a bit confused and baffled at how the ribbon menu worked, but with a few uses, we were able to get the hang of it.