Zimbra has been installed and accepted by all. One feature that I think would be easy(ish) to add on, would be holiday events in the calendar. The appointment schedule key already has a space, that would fit Holiday as an interesting item. This would enable a person to make themselves as on holiday on certain date, or time periods. A couple of extensions to this, could be automatic sending of aproval to the users manager (need an extra item in user details), and even some way of calculating holiday taken / booked so far.
What do you all think? I'll happily add it to bugzilla, but wanted some idea of how silly I was before I submitted it.