WordPress 2.1 has be updated to 2.1.1

The update is a low to medium priority update and:

includes about 30 bug fixes, mostly minor things around encoding, XML-RPC, the object cache, and HTML code.

This is a list of the files changed from 2.1 to 2.1.1:
* wp-includes/post-template.php
* wp-includes/cache.php
* wp-includes/formatting.php
* wp-includes/category.php
* wp-includes/post.php
* wp-includes/version.php
* wp-includes/js/scriptaculous/wp-scriptaculous.js
* wp-includes/js/tinymce/tiny_mce_config.php
* wp-includes/js/tinymce/wp-mce-help.php
* wp-includes/js/tinymce/tiny_mce_gzip.php
* wp-includes/capabilities.php
* wp-includes/cron.php
* wp-includes/functions.php
* wp-includes/bookmark-template.php
* xmlrpc.php
* wp-admin/admin-ajax.php
* wp-admin/admin-functions.php
* wp-admin/custom-header.php
* wp-admin/options-general.php
* wp-admin/edit.php
* wp-admin/index-extra.php
* wp-admin/options-reading.php

It would be irresponsible of me to recommend that you simply update those files. Instead I’ll recommend that you read the upgrade instructions.