just like to say i just did an upgrade of the network edition from 3.01 to 3.1 flawlessly, none of the problems we've seen with the open source edition. also changed the servername/hostname of the zimbra install with libexec/zmsetservername which also performed absolutely flawlessly (PHEW!).
big relief, i had prepared several hours to deal with changing the hostname so i went had had a beer instead
thanks zimbra