With the latest hg version / upcoming v2.1.4 you can do a perfect migration to Maildir using imapc/pop3c backends:
http://wiki2.dovecot.org/Migration/Dsync The main new feature here is the pop3-migration plugin that matches messages from IMAP and POP3 servers together, so that when dsync needs to request POP3 UIDL for some IMAP message it's actually looked up from the POP3 server.
