How does the samba usershare_acl parameter work?
Best hit I got is from: http://devarthur.blogspot.de/2008/05/integrating-ubuntu-hardy-heron-804-with.html
Summarizing:
usershare_acl=Group_SID:access_modifier
To get the SID of the a group use:
wbinfo -n "DOMAIN\group"
SID "S-1-1-0" is Everyone
The access modifiers after the group SID are as follows:
R - read-only
F - full access
D - deny access