cyrus is such a pain, and requires more horsepower on a single box. It is better to run five really crappy cheap servers using courier over NFS
speaking from experience. I have used both extensively, and both are excellent, but I would not leave a cyrus installation in the hands of a newbie, whereas courier is alot easier to support for people who do not specialize in mail servers. I dont think its FUD to say that cyrus is something that an advanced admin may prefer, and a nice thing about courier is that if you find an old spare machine laying around it is very easy to integrate into your mail cluster. And a failed courier box does not affect the rest of the cluster. When a cyrus box fails, there is no doubt downtime, and you need to know how to fix it as opposed to just reinstalling another courier box and copying the config files.
You left out the horsepower bit.
Have you ever ran courier-imap with IDLE support in conjunction with fam? and done the same with cyrus?