I managed to find a big 'Gotcha' with migrating Zarafa from Cos5.2 to 6.4... Make sure your source server is a previous or equal release to the target!!!
I spent (and wasted) some hours during the last week migrating a customer to ClearOS 6.3, but this all went badly at the very end when i realized i was migrating a Zarafa 7.1 database to 7.0 server.... it doesn't work!!!
I'll need to wait for ZCP 7.1 to be released for CO6.3 before i can continue. Thankfully i hadn't gone too far and was able to perform a rollback!
Otherwise, the migration process (as shared by Tim) worked quite nicely as far as i could tell.