Hi,
Facebook like button seems broken at the moment as discussed in this thread I believe it is a problem on the Facebook side of things.
For customized add this button in blog posts you could make a Content Template and then you could easily add it to posts from there (instead of using the feature built into the blog).
Probably this part only should be in the page one time
<script type="text/javascript">var addthis_config = {"data_track_clickback":true};</script>
so if you already have that in the layout.master I think you should leave it out when creating a content template.
AddThis has changed since I last looked at it, when I get a chance I will look into implementing options for their new version.
Hope it helps,
Joe