The Soft Side - Dealing with users
I don't work for Zimbra. I'm an IT Manager who just did a migration of 100 users from Exchange. I wanted my users to try the web client for a few weeks before we made any decisions about Outlook. Here are some of the concerns and how they were answered. This may help you in your migration.
Problem: One end user called in a panic because all of his appointments vanished.
Solution: This is great! He accidentally unchecked the check box in the Calendar page. By checking the box all of his appointments magically appeared.
Problem: An Admin Assistant could not open her managers Inbox like she used to do in Outlook.
Solution: If you are in their Inbox nothing is sacred so get over it and just log into their account. With Internet Explorer and Firefox both being tabbed browsers... have one tab your email and the other his email open.
Problem: When I start a new email and I need to check a schedule, I have to save as a draft, check the schedule and go back to my draft email.
Solution: For most users this would not be a problem, but she does this all day long, see the above solution. We just opened another tab for the calendar in the browser. One tab is his email account. The next is her email account. The third is hers again with her calendar open and her bosses calendar as a shared calendar. There is a feature enhancement in the Zimbra bugs to add shared inboxes, so this may be a non issue.
Dealing with Group Calendars
Group Leave Calendars Old Way - We had a public folder called Leave Calendars. Admin Staff just put things in there.
New Way - Create a Resource called Leave Calendar. Have users Schedule an appointment for the days they will be out and have them meet in the LeaveCalendar Room. Of course it's not really a room, but it works.