Maybe all consider fixing some of the crucial enhancements:-
1. Giving individuals the ability to create distribution list rather than commas separated email address in a single contact. Make the icon of distribution list different from single contacts.
2. Autocomplete on GAL. Even Global Group GAL.
3. Able to see who is in the Group distribution list in GAL or contacts.
4. Select and send to multiple people at the same time.
5. Ability like yahoo to edit the newly sent email address and give it a proper name.
Other inovative stuff is not as important than the common stuff you get on the thunderbird or desktop clients..... maybe good for sales people.
Other than that, Zimbra is just great....