As a follow up to my initial post on the subject, an additional problem that seems to be affecting people with OS X and Cyrus pertains to new log files. Apparently Cyrus roll’s its log file when it exceeds 10MB. For some people the ownership of the new log file is incorrect (root/wheel instead of cyrus/mail) and it causes Cyrus to fail.
This Apple forum thread offers a fix by Matthias Stegner. He suggests creating a bunch of log files in advance:
touch log.0000000002 ... touch log.0000000099 touch log.0000000100 chown cyrus:mail *
This might buy you some time until Apple has posted a fix