Unless you want registered users to be able to edit your blog posts, you should update your WordPress installation to version 2.3.3. It’s a small change, and if you want to you can just replace your xmlrpc.php file with a newer version.
By the way, if you followed the advice in my recent security tips for WordPress post, you wouldn’t have to read about the update on my blog. Instead, you would already be subscribed to the WordPress security/developers’ feed (Atom feed link) that is suitable for subscribing in Google Reader or your favorite feed reader. I highly recommend subscribing to that feed so that you’re less likely to be caught by surprise when there’s a security issue with WordPress.