Some praise:
Timo, I must say I am super impressed with this product. I do free support a few good friends with small businesses running Linux servers (a mix of RH9, Suse9.2 and gentoo) that I dropped as email and samba servers. I found UW-IMAP to be terrible in every way except that using mbox is sometimes nice for old s/w tools. No need for details re UW-IMAP problems. In early 2004 I found courier-imap to be vastly better behaved than UW-IMAP and also much faster once large folders were open. DJB's Maildirs seemed cool, and postfix likes them too, and mb2md-3.20.pl worked great . So everything seemed good and certainly was better. But courier cannot cope with large imap accounts (eg. millions of messages and a few GBytes) where courier-imap grinds to a halt on the initial folder scanning. Cyrus just looks like a big evil beast that needs too much time to learn. Four days ago, this lead me to dovecot. The performance, reliability, configurability of dovecot is amazing.
Timo, I think you could give yourself more credit on something important when selling Dovecot. You write that Dovecot "does not support shared folders". This might turn away some people considering Dovecot. People whom like me do not have/want a good understanding of the imap protocol. I believe you mean that Dovecot does not support shared folders in the technical imap sense of shared namespaces between separate imap accounts. Since Dovecot works beautifully when sharing folders via logging in with the same username more than once. Plus your documentation and config notes imply that this is no problem. IDLE and fcntl locking works great for me. Thank you and good luck!
-Emmett