<h2>Recent comments</h2>
        <?php
        $args = array('status' => 'approve',
                        'number' => 30);
        $comments = get_comments($args);
        $i = 0;
        ?>
        <ul class="recentcomments">
                <?php foreach ($comments as $comment) : ?>
                <?php if ($comment->comment_type == '' ||
                          $comment->comment_type == 'comment') : ?>
                <li>
                <a href="<?php echo get_comment_link($comment- rel="nofollow">comment_ID); ?>"
                   title="<?php echo get_the_title($comment->comment_post_ID);
                   ?>"><?php echo $comment->comment_author; ?></a>:·
                   <span>
                   <?php echo wp_html_excerpt($comment->comment_content, 75);
                   ?>...
                   </span>
                </li>
                <?php ++$i;
                      if ($i > 7)
                        break;
                ?>
                <?php endif; ?>
                <?php endforeach; ?>
        </ul>

Notice the error? The code takes the most recent 30 posts, regardless of post type, and only then filters out pingbacks. So if Wordpress happens to start a flood of pingbacks (for example, as a consequence to post categories being updated), then none of the new non-pingback comments are displayed anymore.

The fix is pretty simple: account for post types when querying the database, and limit the query for a given post type to a given 'number'. Until that's implemented, I guess the reader will have to occasionally suffer from the lack of recent comments.