This is just an fyi. After performing a ./install.sh -u on RHEL4, the mount point defined in /etc/fstab remains. As does /opt/zimbra (this is probably intentional though)
/dev/shm /opt/zimbra/amavisd/tmp tmpfs defaults,users,size=150m,mode=777 0 0
Otherwise I am still working to get it properly installed and functioning based on feedback from the forums. No luck yet.