Just a quick note about the category settings: the phrase "Roles allowed to take part in this category" is perhaps a bit too vague.
I turned off the "banned" members access in my category settings, thinking "I don't want banned members to take part in those categories," not realizing that it would make those categories unbrowsable to people who simple aren't logged in or don't yet have accounts. I now see that by checking the "Banned" box, those users can view the forums without being able to post in them, but I was confused by the terms used.
Just something to think about when tweaking the UI.
This one has been done over before and again. This is the result of mark removing the "applicant" role due to a change back in 0.8.11 or the versions before that causing a conflict along with a DB change.
Mark, I think it's time to drop one of those possible redundant roles and add a "guest" or bring back "applicant" roles or something so people can quit asking this question :)