[Azucar]

I got it to work on vBulletin 4, on the SHOWTHREAD template find:

<li class="popupmenu" id="threadtools">

Add before:

<vb:if condition="THIS_SCRIPT == 'showthread'">
<div style="float: right; padding: 0px 0px 0px 0px;">
<!-- AddThis Button BEGIN -->
<div class="addthis_toolbox addthis_default_style ">
<a class="addthis_button_facebook_like" fb:like:layout="button_count"></a>
<a class="addthis_button_tweet"></a>
<a class="addthis_counter addthis_pill_style"></a>
</div>
<script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js#username=YOUR ADDTHIS USERNAME"></script>
<!-- AddThis Button END -->
</div>
</vb:if>

I'm using the latest AddThis code, on my forum to align the buttons with the rest of the thread tools links, I had to modify the style to this:

<div style="float: left; padding: 9px 0px 0px 0px;">

You play with it until it fits your skin.

This worked for me and it doesn't mean it will for you, you should back up your SHOWTHREAD template before making any changes.