Thanks Nicusor:
Works great. 
I was able to change the width of selected columns on the Posts panel (e.g Title, Author, Categories) with your solution as follows:

    add_action('admin_head', 'my_admin_column_width');
    function my_admin_column_width() {
        echo '<style type="text/css">
            .column-title { text-align: left; width:200px !important; overflow:hidden }
            .column-author { text-align: left; width:100px !important; overflow:hidden }
            .column-categories { text-align: left; width:100px !important; overflow:hidden }
        </style>';
    }