This is what I would like to see in Desktop Client:

1. Possibility to copy emails and contacts between accounts. Currently there is only MOVE option available
2. When I try to write new email the program is searching in global contact book by default, I would like it to look in all contacts in all accounts. It is so hard to use the system, Mozzila Thunderbird is way ahead with user interface, if they would have exchange, contacts, calendar, etc support then I would not use Zimbra as email client at all.
3. Possibility to turn off social tab if I am not using it.
4. Program to remember when I resize columns and windows.
5. Possibility to move accounts up and down
6. Ability to define if new email should come as a separate window or be nested within main window.

It is very nice program but needs a bit of love touch making it easy in use.

Thnx, this is all I can thing about at this stage.