First of all, Zimbra Desktop is amazing. Just keeps getting better every day.
Anyway, we run Zimbra mail servers so for email Zimbra Desktop is perfect. I'd use it for contacts and calendar personally, but we're running the open source version of Zimbra and I have a G1 and haven't bothered with Funambol yet (doesn't do calendar syncing yet for Android anyway). So I can get around that by the fact that Zimbra Desktop will connect to my Gmail account for calendar and contacts which in turn syncs with my G1.
Can I use my Gmail contacts when composing a Zimbra email? The Gmail contacts list neither autocompletes the To: field nor does it show up as an available contact list when clicking on the To: button when composing a Zimbra email.
It would be nice to be able to set a default account for each service - i.e. Zimbra for email, Gmail for calendar, etc.