感谢番茄提供的代码。

<li id="text-5" class="widget widget_text"><h2 class="widgettitle">站点统计</h2>
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<ul>
 <li>建站时间：2012年06月09日</li>
 <li>网站运行：<?php echo floor((time()-strtotime("2012-06-09"))/86400); ?>天</li>
 <li>文章总数：<?php $count_posts = wp_count_posts(); echo $published_posts = $count_posts->publish;?></li>
 <li>分类总数：<?php echo $count_categories = wp_count_terms('category'); ?>个</li>
 <li>评论总数：<?php echo $wpdb->get_var("SELECT COUNT(*) FROM $wpdb->comments");?></li>
 <li>最后更新：<?php $last = $wpdb->get_results("SELECT MAX(post_modified) AS MAX_m FROM $wpdb->posts WHERE (post_type = 'post' OR post_type = 'page') AND (post_status = 'publish' OR post_status = 'private')");$last = date('Y-n-j', strtotime($last[0]->MAX_m));echo $last; ?></li>
 </ul>
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</li>