Zimbra support told us that in order to upgrade our existing Zimbra7 on Ubuntu8 to Zimbra8, we have to do 6 major steps!
1. update Zimbra to latest 7.2.6 for Ubuntu 8
2. upgrade Ubuntu8 to 10
3. reinstall Zimbra 7.2.6 for Ubuntu 10
4. upgrade Ubuntu10 to 12
5. reinstall Zimbra 7.2.6 for Ubuntu 12
6. upgrade Zimbra to version 8!
Anyone successfully upgrade Ubuntu 8 to 12 directly and have Zimbra version 8 installed straight after that? I think it's easier to install a new Zimbra server and migrate the data over, isn't it?