I've got Zimbra 6.0.7 running and have CardDAV configured on both my Mac (Address Book) and my iPhone 4. It works great! Kudos to the Zimbra development team. However, I've noticed one slight issue when viewing address book entries on the iPhone.
When I view any notes that I have assigned to a contact (the vCard "NOTE" field), any place where I have a return character, I see the upper case character "N" on the iPhone instead. The notes don't include any line breaks on the iPhone. I'm guessing this is an iOS bug, but perhaps there could be a Zimbra work-around? When viewing the same contact in the Apple Address Book, it looks fine. And if I export the contact from Address Book, the vCard file shows "\n" (the newline character) as I would expect. The notes also render fine when viewed in the Zimbra web interface.
Anyone else seeing this same issue?