Just wanted to report that there's a slight error in your code. But it wasn't so bad to affect the operation. There's an extraneous
<input type="submit" class="button-primary" value="<?php _e('Save Changes', 'admin-bar-disabler'); ?>) ?>"/>
Noticed this in the multiuser admin page. So I corrected the code there. Been using your plugin for months and just now for WP MU. It's simple and works great for me.