http://wordpress.org/plugins/disablemu/
Hey all, I just had my first submitted plugin approved, and figured I would post here for feedback if anyone cares to take a look.
It's pretty straightforward: it simply writes a few lines to your wp-config.php on activation & removes them on deactivation, the purpose being to "hide" the /mu-plugins directory from WordPress to ensure no arbitrary code can be run from there.
Please be gentle ;) Thanks!