Unfortunately not a solution from my side but some more observations:
- on the iPhone it's seems to be working quite nicely, reflecting the different address books from the Zimbra server
- on OS X Lion the Zimbra address books are not displayed
- groups created in Address Book on the Mac don't appear on the Zimbra server
- entries moved to a group (within the Zimbra account) don't show up on other devices (iOS or Mac OS)
Apparently there is some difference in concept: whereas groups in the Mac OS X Address Book are a subset of all addresses of a given store (ie. Zimbra server) the address books on Zimbra are distinct containers (ie. each address exists in just one container).
Not quite sure how these two concepts can be made to match. The group concept in the Address Book is more like a tag on the Zimbra side of things…