Very nice plugin, and simple to set up.
A couple of issues I'm having:
1. The add to fav link is being injected into the content. Can this be disabled so as to use only the template function for custom placement as per the plugin instructions?
2. The plugin clashes with WordPress SEO and trashes the og: tags. Can this be prevented?
3. The Before Link image could benefit from a switch state. For example, on an un-added post the icon could be grey, and switch to full colour only if the post has been set as fav. That way the icon would actually do its job and indicate to the user what's going on.