I think, it will be good to show some message if site is in Debug Mode...

For example, as i did in *Admin_Controller*:

$this->debug = $this->preference->item('page_debug');
$this->output->enable_profiler( $this->debug );

$this->page->set_title( $this->preference->item('site_name') . ($this->debug ? ' [DEBUG MODE]':''));
}}}

In this example, if site is in Debug Mode then Page Title will be something like that

{{{
<title>Dashboard | BackendPro [DEBUG MODE]</title>

The main idea is to show information that system is in Debug Mode... and not to forget to turn it back in preferences...