Licensing the 2007 Microsoft Office User Interface
Basically anyone* building any* application can utilize the 2007 UI style [Of course you can't write the next Word Open Source project, but you can write any application, as long as it follows the 120+ page Design document (they are even gonna tell you how to make a good design out of your app for once too ;) so good stuff there. ) ].
I don't see why not use the new 2007 UI, heck WinForms guys have been trying to mimic the Office 2003 style since .NET [some were really really bad looking looking applications IMHO].
Jensen Harris's A Office User Interface Blog - Licensing the 2007 Microsoft Office User Interface