As some of you may or may not have seen the first test version of Fedora Core 5 has been release. Now I know Zimbra supports core 3, and a lot of people are running core 4 with miniscual changes. My thought would be to bypass the offical release of Zimbra for FC4, if there were even plans for it, and possibly start looking a offical FC5. That is only if Zimbra is planning on heading that way.

http://fedora.redhat.com/participate/schedule/