Zimbra Desktop 1.0 RC3 Build 1537 should already be on it's way to existing users automatically - but if you still haven't checked out the offline capable client yet, the download is available here.

Some fixes include:
05664 - Webpage in contact don't sync with Y! account
35715 - Disable share folder options for local folders (throws no such item exception)
35770 - RESOURCE_UNREACHABLE in calendar sync
35828 - yahoo address book sync bug
36111 - ParseException thrown for empty IMAP CAPABILITY response
36239 - local to remote msg zimbra sync does not preserve date
36268 - hotmail contact no longer available