snippet - add input...

gistfile1.js

        $(function(){
            $.options = (function(){
                var $self = $(this);
                if ($self.val() === "add"){
                    var $select = $self.closest("select");
                    $select.hide();
                    var $input = $("<input>").blur(function(){
                        var $self = $(this);
                        var newVal = $.trim($self.val());
                        if (newVal.length > 11) alert("Grande demais!");
                        else if (newVal.length == 0) return;
                        else $select.append("<option>" + newVal + "</option>");
                        $select.show();
                        $self.remove();
                    });
                    $select.after($input);
                }
            });
            $("select").change($.options);
        });