How should we setup groups and permissions? The less we have, the simpler it is. I'm pretty sure that too much granularity may result in a nightmare to manage.
Basically, my personal point of view is that nothing should be hidden. Not all users should have the right to modify everything, but I would like that at least everyone is able to read and reply to existing topics, except of course those for which there is really no need to comment (they should be pretty rare though).
Other general rules that I have in mind (some of them are obvious):
- only administrators can post in General (this is reserved for announcements and stuff like that), but anyone can leave a comment
- only administrators and moderators can post in Forum managements, but anyone can leave a comment
- there may be some forums where new users should not be able to post new topic, namely Tutorials (and other ?), but other than that I believe they should have the right to do it.