I am in the process of setting up the Cyrus IMAP server that will eventually replace our UW IMAP server here at The College of New Jersey. In the process of testing Netscape Messenger with the Cyrus server, I found that Netscape Messenger's ACL management is proprietary to their mail server, so I needed an easy way for users to manage their mailbox ACLs (other than converting everyone to the Mulberry email client).
I was impressed with the websieve product from Alain Turbide, but I wanted an interface that was easier for our users to use than the ACL management provide with websieve. We will, however, be using his product for sieve script and vacation management. So, I wrote my own Perl CGI to handle IMAP ACLs, and thought that it turned out well enough to contribute back to the community. We've been using it in a production environment since August 2001. I'm not sure if our user base is using it or even realizes what they can do with it, but that seems like more of a training and PR issue than a technical one.