[Dovecot] Moving mail servers, moving mailboxes

[Gregory Sloop]

So, I've done some searching - but search terms are hard to come by,
that work, for this query.

In short, migrating a RHEL 5.9 server running the back-ported Dovecot 1.0.7
To: Ububtu 12.04 with 2.0.19, I believe.

[I'm not against compiling a more recent version if there's some real
advantage to doing so. But I'd certainly prefer to stay with the
packaged version.]

Most users are POP3, with some leaving messages on the server for a
while.

Other users are IMAP - whole mail repository on server.

---
In an ideal world, I'd like to simply copy all the mailboxes/dirs from one
server to the other. [Local/LAN file copies are possible]

It would be great if the message ID's wouldn't change, so the
read/unread/new etc status all all the messages wouldn't change
between the two servers for POP/IMAP.

---
So, does anyone have a reasonable walk-through for doing so?
Is this a poor idea?
Should I simply set myself on fire now and save everyone a lot of hassle? :)
Would you suggest an alternative, and tell me if it might achieve the
objectives above?

I'm more than glad to take pointers to threads on this topic. I just
haven't been able to dredge this up with my Google-foo.

TIA
-Greg