Es una forma de aumentar los likes de Facebook, ya que muchas personas principiantes, les agrada y dan su like, además de que si está entrando en tu sitio, en porque algún artículo del sitio le interesa. Este pop up me gusta para facebook, hace hasta más elgante nuestro blog.

Para poder poner la caja pop up <me gusta> de facebook para blogger, sigue estos pasos:

Entra en tu escritorio de blogger, luego Diseño, luego añades un gadget y buscas el de HTML/Javascript.

En el gadget que buscaste, pegas el código:

Código HTML:
<style>

/*
ColorBox Core Style:
The following CSS is consistent between example themes and should not be altered.
*/
#colorbox, #cboxOverlay, #cboxWrapper{position:absolute; top:0; left:0; z-index:9999; overflow:hidden;}
#cboxOverlay{position:fixed; width:100%; height:100%;}
#cboxMiddleLeft, #cboxBottomLeft{clear:left;}
#cboxContent{position:relative;}
#cboxLoadedContent{overflow:auto;}
#cboxTitle{margin:0;}
#cboxLoadingOverlay, #cboxLoadingGraphic{position:absolute; top:0; left:0; width:100%;}
#cboxPrevious, #cboxNext, #cboxClose, #cboxSlideshow{cursor:pointer;}
.cboxPhoto{float:left; margin:auto; border:0; display:block;}
.cboxIframe{width:100%; height:100%; display:block; border:0;}
/*


User Style:
Change the following styles to modify the appearance of ColorBox. They are
ordered & tabbed in a way that represents the nesting of the generated HTML.
*/
#cboxOverlay{background:#000;opacity:0.5 !important;}
#colorbox{
box-shadow:0 0 15px rgba(0,0,0,0.4);
-moz-box-shadow:0 0 15px rgba(0,0,0,0.4);
-webkit-box-shadow:0 0 15px rgba(0,0,0,0.4);
}
#cboxTopLeft{width:14px; height:14px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) no-repeat 0 0;}
#cboxTopCenter{height:14px; background:url(http://1.bp.blogspot.com/-TcJGMnSfOC...600/border.png) repeat-x top left;}
#cboxTopRight{width:14px; height:14px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) no-repeat -36px 0;}
#cboxBottomLeft{width:14px; height:43px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) no-repeat 0 -32px;}
#cboxBottomCenter{height:43px; background:url(http://1.bp.blogspot.com/-TcJGMnSfOC...600/border.png) repeat-x bottom left;}
#cboxBottomRight{width:14px; height:43px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) no-repeat -36px -32px;}
#cboxMiddleLeft{width:14px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) repeat-y -175px 0;}
#cboxMiddleRight{width:14px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) repeat-y -211px 0;}
#cboxContent{background:#fff; overflow:visible;}
#cboxLoadedContent{margin-bottom:5px;}
#cboxLoadingOverlay{background:url(http://1.bp.blogspot.com/-PPvu-446sn...background.png) no-repeat center center;}
#cboxLoadingGraphic{background:url(http://1.bp.blogspot.com/-31strss_1-...00/loading.gif) no-repeat center center;}
#cboxTitle{position:absolute; bottom:-25px; left:0; text-align:center; width:100%; font-weight:bold; color:#7C7C7C;}
#cboxCurrent{position:absolute; bottom:-25px; left:58px; font-weight:bold; color:#7C7C7C;}
#cboxPrevious, #cboxNext, #cboxClose, #cboxSlideshow{position:absolute; bottom:-29px; background:url(http://1.bp.blogspot.com/-FiJ_Xz7txE...0/controls.png) no-repeat 0px 0px; width:23px; height:23px; text-indent:-9999px;}
#cboxPrevious{left:0px; background-position: -51px -25px;}
#cboxPrevious.hover{background-position:-51px 0px;}
#cboxNext{left:27px; background-position:-75px -25px;}
#cboxNext.hover{background-position:-75px 0px;}
#cboxClose{right:0; background-position:-100px -25px;}
#cboxClose.hover{background-position:-100px 0px;}
.cboxSlideshow_on #cboxSlideshow{background-position:-125px 0px; right:27px;}
.cboxSlideshow_on #cboxSlideshow.hover{background-position:-150px 0px;}
.cboxSlideshow_off #cboxSlideshow{background-position:-150px -25px; right:27px;}
.cboxSlideshow_off #cboxSlideshow.hover{background-position:-125px 0px;}
/*-----------------------------------------------------------------------------------*/
/* Facebook Likebox popup For Blogger
/*-----------------------------------------------------------------------------------*/
#subscribe {
font: 12px/1.2 Arial,Helvetica,san-serif; color:#666;
}
#subscribe a,
#subscribe a:hover,
#subscribe a:visited {
text-decoration:none;
}
.box-title {
color: #3B5998;
font-size: 20px !important;
font-weight: bold;
margin: 10px 0;
border:1px solid #ddd;
-moz-border-radius:6px;
-webkit-border-radius:6px;
border-radius:6px;
box-shadow: 5px 5px 5px #CCCCCC;
padding:10px;
line-height:25px; font-family:arial !important;
}
.box-tagline {
color: #999;
margin: 0;
text-align: center;
}
#subs-container {
padding: 35px 0 30px 0;
position: relative;
}
a:link, a:visited {
border:none;
}
.demo {
display:none;
}
</style>

<script src='https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js'></script>
<script src="http://yourjavascript.com/11215013191/jquery.colorbox-min.js"></script>
<script type="text/javascript">
jQuery(document).ready(function(){
if (document.cookie.indexOf('visited=true') == -1) {
var fifteenDays = 1000*60*60*24*30;
var expires = new Date((new Date()).valueOf() + fifteenDays);
document.cookie = "visited=true;expires=" + expires.toUTCString();
$.colorbox({width:"400px", inline:true, href:"#subscribe"});
}
});
</script>
<!-- This contains the hidden content for inline calls -->

<div style='display:none'>
<div id='subscribe' style='padding:10px; background:#fff;'>
<h3 class="box-title">Mantente en contacto con nosotros a través de Facebook. Sólo presiona el botón Me gusta <center><p style="line-height:3px;" ></p></center></h3> 
<center>

<iframe src="//www.facebook.com/plugins/likebox.php?href=http%3A%2F%2Fwww.facebook.com%2Fpages%2FEstatriste%2F186903574749125%3F&amp;width=300&amp;colorscheme=light&amp;show_face s=true&amp;border_color=%23ffffff&amp;stream=false &amp;header=false&amp;height=258" scrolling="no" frameborder="0" style="border:none; overflow:hidden; width:300px; height:258px;" allowtransparency="true"></iframe>

</center>
</div>
</div>
Para que funcione con tu fan page, debes de cambiar la url que aparece en el Iframe, al final de todo el código (http%3A%2F%2Fwww.facebook.com%2Fpages%2FEstatrist e%2F186903574749125%3F). eso es todo y bien fácil de hacer.

Regards.