I've dumped the old Courier IMAP software that I had been using for POP/IMAP in favor of Dovecot. I had no real reason to do so, Courier IMAP was running fine (though I did have issues during install last time around). However, Dovecot does seem to be the new hotness, so I decided to give it a go.
Much has been said elsewhere about Dovecot's superior performance, but with my little server that isn't much of a concern, but there are fewer files to mess with, and the overall operation does seem more streamlined. A single process handles authentication, IMAP, and POP, spawning what it needs automatically.
The tricky part was integrating with Postfix Admin and the virtual user setup, but there were guides online that assisted with most of this. As I had stretched this upgrade process out over several weeks of fiddling with the server, I can't point to any single definitive source for upgrade advice, but some Googling will find what you're looking for.
My major headache came with the courier-dovecot-migrate script, and its insistence that I had no mailboxes. Online advice claimed that this was normal, and that it would work when the actual conversion was done, but even then it still reported zero mailboxes, but apparently DID do its thing.
The last hurdle was specifying the exact path for my virtual users, in my case, /var/mail/vhost/%d/%n, and after that it was working fine.
There are some good debugging options, which helped greatly.