I have recently set up a second Zimbra site and it's the Open Source version. Everything seems to be working fine so far except that when I'm in the Admin web interface, querying for users accounts and for mailbox quota's takes at least 50 seconds and maybe longer.
There are only 3000 accounts on this machine and users are not accessing yet so there is no load on the machine yet. The server has 32GB of memory and has multiple cores and the storage is on a RAID 10 array.
Going into an individual user account seems to be fine and there is no slow down at all.
I have stopped and restarted Zimbra and have looked at a few log files but everything seems to be running fine.