When I list al groups I see one called 'nogroup'. What is this for? Is it supposed to be least privileged one or something?  I'm using ubuntu 11.04. 
what is 'nogroup' group's purpose
permissions;group
nogroup is the group analog to the nobody user.  It is used for unprivileged processes so that even if something goes wrong the process does not have the permissions to cause any serious damage to an important user or group.