I recently had a need to include a document in two categories in a SharePoint document library. I did not want to have duplicate copies of the document in the library. A Google search quickly (after I figured out the right search terms) lead me to mindykelly’s blog entry on SharePoint Blogs. This is turn lead me to Todd Klindt’s Blog entry One document, multiple Document Libraries which documents these steps with pictures. There are also a number of useful comments to his post.
Through one of those comments I learned that metadata can be attributed to a linked document by using “edit in datasheet”. This allowed me to populate the metadata columns showing in the view ensuring the linked document was grouped in the category as we wanted.