I often find that I have lots of documents open and can't always remember if I opened them from an email attachment, My Documents or a SharePoint site. I would often use the "File Save-As" menu just to see where the file was opened from. It turns out that you can add this information to the Quick Access Tool Bar by following these steps...

http://office.microsoft.com/training/training.aspx?AssetID=RP102338321033&CTT=6&Origin=RP102338311033

You can also copy the document url from here for use in other documents or emails.