$this->crud->add_description($column_name, $column_description);
[attachment=284:Untitled-1.jpg]
For now i use this like:
->display_as('post_tags','Column Title <small>column description</small>');
and style it.
I know that i can achieve this with callback function but it will be hard for us to do this for all fields. you know time is money huh

I'll be appreciated if you add this in new version.
Thanks in advance.