I'm really pleased I found Zimbra (I only installed yesterday) and whilst remembering int is still in beta, I'd like to suggest more visibility for appointment reminders.
The tought bubble coming from the system tray is so quick I have only just realised what it was as I have other notifications going on there.
As for having a detail of the appointment come up - it only displays when i'm actually viewing the calendar the appointment is stored in (I have multiple accounts stored in Zimbra). Since I am already viewing my calendar, this is not where I need to have a clear reminder!!
Any chance the appointment detail window (the one I need to dismiss or snooze) could pop up over all other windows. Other PIM programs have this as standard and it is precisely when I am engrossed in another program that I really need the reminder!