I'm setting up 40 blade servers each with direct access to a shared FC SAN volume and mounted GFS and serving it up via both SAMBA and NFS to ~10 virtual machines (XEN and VMWARE) local to that blade. I don't expect the unix VM's to use SAMBA (exception might be HOMEDIRs) nor the Windows VM's to use NFS, but otherwise it's active/active. NFS will also be used to rootless boot the XEN/VMWARE virtual machines that run Linux.
So that's 40 independent SAMBA servers all potentially serving the same files located on the common GFS volume. Think I'm headed for trouble? That config would come in handy.