Well, today, in getting ready for next year, I deleted all users who weren't enrolled in any courses this year, keeping information for quizzes, etc. I also updated all our course ids to reflect their new ids in our SIS.
Then, I went to front page roles, clicked on student, and saw that even the users I'd deleted were still listed, so I highlighted the entire list of users in the student role, and clicked the button to move them back out. Our Moodle installation was then unavailable to ANYONE for about three minutes as it processed through all the roles. I've attached a screenshot of what I got (for size purposes, I've only given you a small bit of this - it just continues for several hundred courses!). I THINK I'm getting this because I use database enrollment and it's tying into all the courses the students MIGHT be in, but I'm not sure.
I think the solution for this would be a checkbox in the front page settings, or a string in config.php, something along the lines of 'All authenticated users are front page students', and I thought I remembered something along those lines, but I can't find it. Does anyone know about this, or should I file this in the tracker as an Improvement request?