I've searched around a little, and found various solutions to specific problems... however, I haven't seen a sticky/guide to backing up and restoring to a new machine.
What we're planning on doing is:
1) Install SME on the new machine, with its network cables unplugged.
2) Use the admin console to configure it exactly as the old SME box is.
3) "Backup to desktop" the old SME box's config from Horde.
4) Power down the old SME box.
5) Plug the new SME box into the ethernet switch.
6) "Restore from desktop" in Horde.
7) Reboot the new SME server.

Pray that everything is restored.
Does this sound right? I realise that this will not backup things like the SSH daemon configs, and such... but all the users and pop3/imap/smtp settings will at least be there...?
If you have any helpful links, I'd appreciate those.
Thanks