First off, I would like to say that your product is great. It's got all of the features I could ever need, and it takes about 5 minutes to setup. I couldn't be more impressed.
I do have some recommendations (these may have been addressed elsewhere).
1) When you install Zimbra on a server, Zimbra takes over. It binds to all IP addresses, it pretty much owns your entire box. There will be no serving of http/https while zimbra is around. Is there a way to bind zimbra to only 1 IP? Would it just simply be editing the iptables redirects?
2) Fedora and RHEL are great and all, but I would really like to run Zimbra in a Solaris 10 zone.. This would rule out the need for #1, because Zimbra could own the zone and the server could have other zones for web serving and such.. This is also a more secure model since if my webserver zone gets hacked, the attacker doesn't instantly get access to my email.
Keep up the great work! I'm definitely spreading the word to my friends.