This is a nice way to achieve something simple without the use of a plugin. You can show off your latest comments in your sidebar, with the gravatar. Just paste this into your sidebar.php

<?php     $comments = get_comments('status=approve&amp;number=5'); ?> 
<ul> 
<?php foreach ($comments as $comment) { ?> 
<li> 
<?php echo get_avatar( $comment, '35' ); ?> 
<a href="<?php echo get_permalink($comment->ID); ?>#comment-<?php echo $comment->comment_ID; ?>" title="on <?php echo $comment->post_title; ?>"> <?php echo strip_tags($comment->comment_author); ?>: <?php echo wp_html_excerpt( $comment->comment_content, 35 ); ?>... </a> 
</li> 
<?php }  ?> 
</ul>