Performed the upgrade with no issues whatsoever on Ubuntu 8.04.3 x64. Installer went quickly, all my normal tweaks after the install were reapplied easily.
Drag 'n Drop working flawlessly for our users on Firefox 3.6 ... they are very happy about that feature.
Child accounts are working great again, and our sales team is delighted.
Thanks to the Zimbra team for a job well done!