Hi
Very great to discover this tools and just bought a one year bundle licence for a server migration 
Source : debian4 / ZCS OSE 6.0.14 / 32bits
Destination : ubuntu 12.04 LTS / ZCS OSE 8.0.2_GA_5569.FOSS / 64bits
i started the migration using the follow path in the wiki :
- despite i don't have the zimlet showing in the administration panel on the source server, just started exporting All in command line which gave me 14GB on data on /opt/zimbra/backup
- mounted the backup on the destination server using sshfs on /mnt/export.
Zimbra user as full access on it (ok with su - zimbra; ls /mnt/export)
- went to admin panel => zextra => backup => import => /mnt/export
- got the first notification : 11:36, External Restore Started
- and then 11:37: External Restore Running
- 11:37 : External Restore completed
All accounts were restored
but they all have empty mailboxes !!! (at least the one i was intersted in)
Retried 3 times and same result...
also reformatted destination server and reinstaller zcs 8 and zextra, same result
any idea ?
thanks.