Actions usually support the following (if you are creating your plugin using a class based approach):
add_action('admin_notices', array(&$this, 'emailNoticeGUI'));
wp_schedule_event does not support this kind of triggering. Is there any way I could do this, but still use a class based approach? What are the alternatives? I would like to schedule a hook upon plugin activation, but the activation logic is also based in the class itself.