Edit in JSFiddle

 var divs = $("div").get(); // unique() must take a native array

 // add 3 elements of class dup too (they are divs)
 divs = divs.concat($(".dup").get());
 $("div:eq(1)").text("Pre-unique hay " + divs.length + " elementos.");

 divs = jQuery.unique(divs);
 $("div:eq(2)").text("Post-unique hay " + divs.length + " elementos.")
     .css("color", "red");

<title>jQuery.unique demo</title>
<div>Hay 6 divs en este documento.</div>
<div></div>
<div class="dup"></div>
<div class="dup"></div>
<div class="dup"></div>
<div></div>

{
    color:blue;
}