Conditionally add admin notes

functions.php

<?php

//* Conditionally add admin notes


function wpspeak_admin_notice(){
    global $pagenow;
    if ( $pagenow == 'plugins.php' ) {
         echo '<div class="updated">
             <p>This notice only appears on the plugins page.</p>
         </div>';
    }
}
add_action('admin_notices', 'wpspeak_admin_notice');

Credit: http://wptheming.com/2011/08/admin-notices-in-wordpress/