Here's a categorized Table of Contents to help you discover posts you might find interesting or relevant.

If you're new here, I'd recommend that you start reading at the top.

Why a New UI for Office 2007?

Presentations

Overview of the New UI

Ribbon UI Elements

The Size of the Ribbon, Screen Real-Estate, Ribbon Scaling, and Minimization

Migrating to Office 2007

UI Themes and Visuals

Keyboard Control of the Ribbon

New Fonts for Office 2007

Customizing Office 2007

From First Sketches to the Final Design

Design Tenets

Design Ponderings

An Inside Look Into UI Design, Usability, Development and Testing at Microsoft

Office Themes

New Features in Office 2007 Involving the New UI

Miscellaneous

The Office 2007 UI team