I've installed the plugin, added my App ID and Secret from Facebook and have configured the other settings.
However, all that's appearing in my source code is:
<div class="wdfb_like_button"><fb:like href="http://smokefreediary.com/about/" send="true" layout="standard" width="300" show_faces="true" font=""></fb:like></div>
No Like button at all.
The code can be found on this page: