Very good initiative; 3rd Parties can now license the 2007 Microsoft Office UI to develop their own applications and as far as I understand this is for free. Ofcourse there are rules as this has been a huge investement for Microsoft as you well understand. The document mentioned below provides you with more details on the licensing and the program :
This information is provided to assist third parties to incorporate the Office user interface designs into their own applications. The license provides the terms for third partners that wish to take advantage of user interface investments in the 2007 Microsoft Office suites and license these investments for their own use. The FAQ gives more details about why we are licensing the user interface and the benefits it gives to our customers and partners.