Facebook Check In API

This technique is now deprecated.

This used to tell Google how to index the page.

https://developers.google.com/webmasters/ajax-crawling/

This technique has mostly been supplanted by the ability to use the JavaScript History API that was introduced alongside HTML5. For a URL like www.example.com/ajax.html#!key=value, Google will check the URL www.example.com/ajax.html?_escaped_fragment_=key=value to fetch a non-AJAX version of the contents.

via Facebook's Platform Updates:

Change in Session Redirect Behavior

This week, we started adding a fragment #____=____ to the redirect_uri when this field is left blank. Please ensure that your app can handle this behavior.

To prevent this, set the redirect_uri in your login url request like so: (using Facebook php-sdk)

$facebook->getLoginUrl(array('redirect_uri' => $_SERVER['SCRIPT_URI'],'scope' => 'user_about_me'));

UPDATE

The above is exactly as the documentation says to fix this. However, Facebook's documented solution does not work. Please consider leaving a comment on the Facebook Platform Updates blog post and follow this bug to get a better answer. Until then, add the following to your head tag to resolve this issue:

<script type="text/javascript">
    if (window.location.hash && window.location.hash == '#_=_') {
        window.location.hash = '';
    }
</script>

Or a more detailed alternative (thanks niftylettuce):

<script type="text/javascript">
    if (window.location.hash && window.location.hash == '#_=_') {
        if (window.history && history.pushState) {
            window.history.pushState("", document.title, window.location.pathname);
        } else {
            // Prevent scrolling by storing the page's current scroll offset
            var scroll = {
                top: document.body.scrollTop,
                left: document.body.scrollLeft
            };
            window.location.hash = '';
            // Restore the scroll offset, should be flicker free
            document.body.scrollTop = scroll.top;
            document.body.scrollLeft = scroll.left;
        }
    }
</script>