FWIW, I added mode=755 for the following reason. Sorry for the unfortunate side effect of that change.
[ Evan Dandrea ]
* Add mode=755 to the tmpfs mount that becomes / in the unionfs mount
so that / in the live filesystem does not end up with 777 permissions
-- Evan Dandrea <email address hidden> Wed, 26 Mar 2008 14:47:06 -0400