sergofedor06,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
#ss, .del_variant{
cursor: pointer;
}
.control-group:nth-child(1) .del_variant{
display: none;
}
</style>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<script>
$(document)
.ready(function () {
var variant = $('.control-group')
.clone(true);
$('#ss')
.click(function () {
$(variant)
.clone(true)
.appendTo('#variants')
.fadeIn('slow')
.find("input[name*=name]")
.focus();
if($('.control-group').length == 5) $(this).hide();
});
$(document)
.on('click', 'a.del_variant', function () {
$(this)
.parents(".control-group")
.remove();
if($('.control-group').length < 5) $('#ss').show();
});
});
</script>
</head>
<body>
<div id="variants">
<div class="control-group" >
<label class="control-label">Username</label>
<div class="controls">
<input type="text" placeholder="Username" name="name[]"> <a class="del_variant">X</a>
</div>
</div>
</div><span id="ss">Добавить вариант</span>
</body>
</html>