hi there.
I have been using this plugin until now: http://rizapn.blogsome.com/2008/10/19/updated-custom-css-plugin/
the difference I see, is that your plugin stores the css in the DB while the other one creates actual files. I like the DB solution more.
But the other one, is able to create one file for each theme, while your css applies to any theme...
I am not sure what the better solution is, anyway, I like that you filter the css to scan for dangerous code, while I am unsure if the other one does.
maybe some other people using wpmu can contribute some of their thoughts?