Unfortunately there is a bug in the widget. Open perfect-quotes/includes/widget.php and search for
$title = apply_filters('widget_title', empty($instance['title']) ? __('Perfect Quotes') : $instance['title'], $instance, $this->id_base);
and replace it with
$title = apply_filters('widget_title', empty($instance['title']) ? $instance['title'] : $instance['title'], $instance, $this->id_base);
Now you can leave the title empty and there will be no default title.
This should be fixed by the author. Great plugin anyway. Thanks and continue the good work.
I updated the code with the following line as @mensmaximus’s code was redundant. Thanks for the heads up though!
$title = apply_filters('widget_title', $instance['title'], $instance, $this->id_base);
