My installed WordPress 3.1.3 told me that this plugin (WordPress Related Posts by Denis from fairyfish.net) had been updated to 2.0, but the update is for a *different* plugin (by Thamizhchelvan from wphelpforum.com).
I updated it and it broke my site! After a couple hours of frantic searching, I finally found this plugin and reinstalled. Phew!
Advice for anyone with WordPress Related Posts by Denis from fairyfish.net installed: Do NOT upgrade the plugin, even if WP tells you to.
WordPress peeps: Is something fishy happening here?