Our upgrades were smooth for the Proxy, MTAs and LDAP servers, but the Mailbox servers were a little bumpy.
For some reason, Zimbra required us to modify our hosts file. When we did this on the other systems, everything went fine. When we did it on the Mailbox servers, one of them got upset:
After I restored the /etc/hosts file back, I then tried to start Zimbra and got this error:
Upgrading from 5.0.21_GA_3150 to 6.0.5_GA_2213
Stopping zimbra services...done.
ERROR 1033 (HY000) at line 1: Incorrect information in file: './zimbra/config.frm'
Thu Feb 18 00:24:19 2010: Error while running '/opt/zimbra/bin/mysql --user=zimbra --password=************** --database=zimbra --batch --skip-column-names'.
I found some posts about DB Version Mismatches, which said to run the setup again, which we did and it corrected the problem.
2010-02-18 00:42:03,940 ERROR [main]  Versions - DB Version Mismatch: ours="64" from DB="53"
2010-02-18 00:42:03,940 FATAL [main]  system - Data version mismatch. Reinitialize or upgrade the backend data store.
The last problem we had was that the new convertd was selected (I forget it we chose to run it or if it defaulted YES). The new convertd caused some anomalies with search results. We haven't turned this off - instead we've done a few Mailbox Reindexes which seems to work (rather slowly) with correcting the search indexes.