That was one idea that I was considering doing... but what I really want is for users to be able to create forums, edit them, change some settings...
Each board will be reinstalled every hour or so as an added precaution.
If you're going to have a crontab running that will just run "rm -fr *" on the public_html directory, then untar a backup file, with the database settings and stuff already pre-configured, then I see absolutely no point in limiting what each of the demo's can do. I believe that a better solution is to create a script called resetdemo.php or something like that, which has the ability, when executed to reset the demo's by manually running the crontab or deleting, then extracting the files by some other means, though by doing this in PHP you will most likely run into permission issues if you try to edit the files manually via FTP. The only real solution for doing it via a web-script would then become perl. The link to this reset script could be in the error pages of the forums. Just edit the templates for the error.
My solution is more work, but in the long run it's worth its weight in gold.