So it seems that my version of Microsoft Office is released under the GPL license:
Just kidding, obviously. But for some reason, Office stores its registration agreement in the registry under this key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\11.0\Registration\{90110409-6000-11D3-8CFE-0150048383C9}
The text is base64-encoded unicode, and is the license agreement that can be accessed by the blue hyperlink in the "about" dialog.
This .reg file might change the license agreement to GPL for you, if you're so inclined.