I have just uploaded version 1 of my plugin, Fun with Categories.
Fun with categories adds a method to search for posts that have both of two specified categories; for example, a post containing photographs of your cat might be assigned to categories, ‘Photos’ and ‘Cats’. To view all photographs in both of these categories you can use the URL: http://yourblog/categories/photos/cats/
The update is very minor. I have changed the way the SQL is generated so that it uses the built in $wpdb->posts function instead of containing the string, ‘wp_posts’. This makes sure it can support blogs where the database prefix has been changed.