I am using the FOSS version, since I'm small and don't need the extended features (although they do look nice).. but I have a multi-server setup with 2 servers, both in different geographical locations.. both are are MTA's and Mailbox servers, but only one was the LDAP server. I decided to setup the 2nd as an LDAP replica, and I just have to say that it was a lot easier than I thought it would be. I took the master server offline and the replica ran off itself serving logins and accepting mail through the MTA. It's working perfectly.
Just wanted to post a "great job on Zimbra guys!" thread. It's made my home email setup a lot easier to deal with.