I refer to my thread over here where I found one of my plugins kept adding a link to WordPressSupplies to my blogroll automatically.
After searching my plugin code, I found this one does in fact check to see if their link is in your blogroll and then adds it. I saw no mention of this anywhere in the install page, if you're going to add links to my website I'd appreciate knowing about it.
From what I can tell, themes and plugins from WordPressSupplies do this as well, so I'd be wary of using anything from there.
Line #143 of auto-tagger.php contains the following code.
if($wpdb->get_var("SELECT COUNT(link_id) FROM $wpdb->links WHERE link_url='http://wordpresssupplies.com/'")==0) wp_insert_link(array('link_name' => 'WordPress Themes', 'link_url' => 'http://wordpresssupplies.com/', 'link_description' => 'Download Free WordPress Themes and Plugins' ));