In the latest update of WordPress, to version 3.0, I noticed one link element being added in my site’s head section. I personally prefer to see no change in the coding after updates: the coding that I am talking about is the code we see via using browser view source code option.
This element looked something like this:
<a rel="shortlink" type="text/html" href="http://www dot yoursite dot com">
This element includes a shorter version of the link to your site/blog/post. And I think it helps the users when it comes to using social bookmarking and similar types of sites.
Anyway, in order to block this element, you need to put this code:
remove_action('wp_head', 'wp_shortlink_wp_head', 10, 0 );
In function.php file: you can find this file in your currently used theme folder: