I just stumbled across a quite informative article about the Office 2007 Document Inspector API.

http://msdn2.microsoft.com/en-us/library/aa338203.aspx

Basically, it's a new API for removing metadata from Office Documents. It's extensable, which is cool.

But it's woefully underpowered as is, and it's only applicable to Office 2007 installations.

At any rate, a decent article on the subject.