Our experience has been similar. We did a test pilot of 5.0.0 (starting with RC1 through GA) way back when. During the pilot, a bunch of issues were found and filed as bugs. We also found bug entries that corresponded to issues we were having, so we added comments to those bugs, and voted for them.
After the pilot, we decided not to go with Zimbra. That was about a year ago. Yesterday, I logged into bugzilla as we are againg piloting Zimbra, and over half of the bugs we voted for were marked as complete.
If you aren't willing to spend the time documenting issues and entering bugs and participating in the resolution process, then you really can't complain.
