I was contemplating how to manage document storage policy-wise with the document/briefcase systems in Zimbra and our local samba office file shares.
The best thing would for Zimbra to web-link to the samba share and documents can be downloaded/uploaded via Zimbra from the Samba shares.
There is a great script that I use: SSLBridge - Open Source Linux VPN software - Samba Browser
It is a very ajaxy web-based vpn so u can access file shares on a samba server via the web. This is how we currently keep documents centralized.
Maybe sslbridge could be a good basis for integrating this feature in zimbra!