Hi
I really appreciate feedback. We're on a time-crunch to migrate from a debian 5 box w/ dovecot 1.1 to a debian 6 box w/ dovecot 2.0.9 (built from source).
I would have thought if time is tight then stick with what you know and migrate later? If you aren't building your new box as a virtualised container of some sort then stop and consider that to be much more desirable... With a virtualised install you can easily spin up an alternative config and more easily migrate the format of the data separately to the config of the server?
Oh, I'm also a huge fan of the "proxy" feature which allows you to spin up a new machine/config, then migrate users across slowly rather than one big bang. You can use it with your current migration to test the upgrade for example?
According to the wiki, your answer to the dbox question is probably best given here: http://wiki2.dovecot.org/MailboxFormat/dbox
Good luck
Ed W