Webmin works well for allowing non-technical people (like school principals and teachers) to do limited admin work on servers (like managing user accounts and quotas). And for allowing limited admin access to semi-technical people (like Windows/Novell admins accessing Linux servers).
However, it does require a lot of planning and configuration and what-not. By default, it uses a "everything is permitted" security settings. It's up to you to limit what people can do.
We've been using it for almost a decade now, on all of our school servers. Initially to ease the migration from Novell to Linux, as everyone was used to a GUI admin tool. Then to allow more and more non-techy people to manage the things they need.
So far, no major issues. The only one was allowing a tech teacher to have root-level access to a file manager ... which he then used to completely hose the /home filesystem. Thankfully, that was after we starting using rsbackup, and it was a very simple rsync operation to fix everything.
