Hello,
UW-Imap has a (questional, but for me useful) feature to slurp all mails pending in /var/mail/uid into the user's INBOX whenever the user successfully logs on and the INBOX is not configured as /var/mail/uid.
The usefulness for me is that users have a relatively small quota, so the noisy "over quota" messages pop up for everyone now and then, regardless how frequent one reads the mail. When I now set a large quota for the "pending INBOX", where the user (aka dovecot) can only delete mails from, I circumvent those messages, prevent that users use the (large) INBOX as yet another place to pile up data (the user does not know about the pending INBOX at all) and let the users have "full" control over their folders.
The disadvantage is that it works for "real" users only. Another disadvantage is that one would expect "LDA"-features in the server portion of Dovecot, e.g. Sieve :-), or the server would need to spawn the Dovecot-LDA somehow.
(Next thing is that, currently, the mails are delivered into the home directory of the users, what leads to several annoyances when someone is away for some time and finds his home directory locked, because the mass of mails locked the directory. Mostover, those IMAP servers I ran so far didn't allowed the user to delete a mail via IMAP often, because some temp or arbitary file couldn't created in the IMAP root. Because the user is already logged on onto Dovecot, there should be less problems deleting mails when the quota exceeds while slurping them in. At least I had extremly good experiences with this mechanism, when I used UW-Imap and the INBOX was located as mbx in the user's homedirectory.)
Bye,
-- Steffen Kaiser