we are evaluating zimbra as a one for all replacement for our separate cyrus IMAP and MS Exchange installations. A feature used heavily in our workflows are the shared or workgroup folders you can have in IMAP servers.
I've found no equivilant in zimbra yet. Maybe we can substitute it with shared accounts, though this is not an optimal replacement.
But what we really need to have is to address mail folders directly, like user+News.Control_Done.email@example.com on our cyrus imap. We do this from alias files, scripts, procmailrcs and other sources and need an equivilant feature in zimbra.