As promised in my iMoot2012 'UOW's Moodle 2 Journey' session here is a link to the GoogleDoc of permission capabilities we used for version 1.9 at Waikato.
UOW Moodle 1.9 role permissions - http://goo.gl/elcBP
As part of our Moodle 2 upgrade process we duplicated our v1.9 site and made it available in read only mode while we upgraded the duplicate to 2.0. This was achieved by altering the Authenticated User role's editing capabilities to "Prohibit" which overrode other role's editing abilities.
I hope this is useful to others