Request Tracker Import/Export
As of January 2008 there didn't appear to be much by way of support for importing/exporting tickets out of one RT instance into another. I needed to merge from one into another, so I wrote the code to do this.
Export
RT does come with a very basic dumper, however, it's pretty much core configuration only. rt-ticket-dumper is a very basic XML exporter. It will export the details of a Ticket, Transactions, Attachments and Links. It does not dump the queue configuration, and the mapping at the start of the file is so that you can create the queues in advance on the target instance and map the ids from one to the other.
All users are referenced by email address. This is to simplify matters, it woudln't be massively difficult to export and import Users as well, but in our case it wasn't needed.
Import
rt-ticket-importer is a very basic XML importer. It will import the details of a Ticket, Transactions, Attachments and Links. It does not import the queue configuration. It is worth noting that if a user in the target system does not have the "OwnTicket" privilege then it will give the ticket to nobody.
All users are referenced by email address. They are literally loaded by "CreateOrLoadByEmail().
Somewhere in the core RT or DBIx::SearchBuilder there is a nasty bug which means that the Ticket::Import() function doesn't actually work properly if you don't provide an id and EffectiveId. Ticket_Local.pm contains a horrible nasty hack around this.