For the calendar side of things what would be really good is if you could have some sort of 2-way CalDAV sync going on between Zimbra and Exchange.
But I believe Zimbra only does 1-way sync with CalDAV at this stage... it's a CalDAV server but not client.
Not sure about CalDAV support in Exchange though.
We also had a very extensive Exchange Public Folder system but mainly mail items. We migrated from SBS 2003 to Zimbra last year and I've been able to get close to the same level of usability. I have an account called
shared@domain.com which exports all shared resources.
But from an admin perspective there's a few annoying bugs/RFEs that I'd love to see implemented in Zimbra's sharing to make it equivalent to Exchange...
Bug 16411 – RFE: Bold/Italicize parent folder when subfolder contains unread mail Bug 24567 – Support per-user seen status for shared mail folders Bug 24727 – Shared mail folder delete warning Bug 43733 – Can't move subfolders in shared email folder Bug 49941 – Option to make shares persistent when shared through distribution list, choose mount point name/color ... very important!
It's particularly worrying that a user can delete the entire shared mail heirarchy, it goes to their trash, then if they empty trash... it's gone.
Sorry to have not been of more help on the calendar sync thing though.