We're about to make Zimbra to our strategic Groupware system for ourselfs and for our customers.
The only thing which urgently should be possible is a real global address list. In most cases in switzerland we have companies with about 20 to 50 max 100 employes but a huge central customer address list (in our case 1800 contacts) which is shared across the company.
We made a workaround with a shared contacts folder across the user accounts (see Set default address book to imported one)
But for the mobile access we need to have access to this shared addressbook through ActiveSync Global Addressbook access.
So we need a workround to anyhow configure the activesync part that way that the mobile gal access searches this shared addressbook. If this is solved, we have here a potential of about 500 paid mailboxes. But this function (specially in combination with sugar crm, (we wrote a integration for sugar->zimbra)) would be a decision maker.