Zimbra source code was made available again as a GIT repository recently.
After many fixes to the current official documentation I have finally managed to build Zimbra OSE 8.0.6 and Zimbra OSE 8.0.7 in an Ubuntu 12.04 64 bit system . The original instructions are in Spanish but the commands speak for themselves. Just make sure you use a new minimal installation so that you don't loose any important contents.
Feel free to adapt it to a Zimbra Wiki page so that it helps more people.
Feedback is welcome.
Compilar Zimbra OSE 8.0.6
Compilar Zimbra OSE Ironmaiden (8.0.7)