Here is a post in forums.iis.net that is worthy of an complete article.

http://forums.iis.net/t/1150447.aspx

It addresses caching on a UNC path where the server is a non-Microsoft OS file server.  It's a Novell server using CIFS.   If you have documents on a Samba or CIFS server, this article contains some good information.

Cheers,

Steve