Customize the Office user interface in Office 2010

This article lists resources that will help you customize the Microsoft
Office Fluent user interface (UI) in Microsoft Office 2010 applications.

Microsoft introduced the ribbon extensibility model in the 2007 Microsoft
Office system as part of the Office Fluent UI. This was a new way to customize
the user interface and create custom tabs and groups that were specific to
users’ needs. Office 2010 extends the span of the UI extensibility platform by
providing support for customization of the new Microsoft Office Backstage view.

http://technet.microsoft.com/en-us/library/ff468686.aspx#section2

Deploying a Customized Ribbon and Quick Access Toolbar in Office 2010

Summary: Deploying a customized Ribbon and Quick Access
Toolbar is an often requested action for developers and administrators. Learn
how to deploy a customized Microsoft Office UI to users, place the file at a
particular location, and restrict further customizations. (8 printed pages)

http://msdn.microsoft.com/en-us/library/ee704589(office.14).aspx