I've received several warnings from facebook recently. The warnings say something like:
Your app, [App Name] has not enabled the migration for the July 2013 Breaking Changes.
[App Name], is currently using the following deprecated features:
Social Plugins (Like Button, Like Box) without absolute URL's in their `href` parameter.
Like buttons and other social plugins produced by Drupal for Facebook already use absolute hrefs. I have yet to find a single social plugin using a relative href in any of the apps which facebook is warning me about.