Removing the “Website” Field from Comments and Replies?

Create a file in wp-content/plugins/ with this code:

<?php
/*
Plugin Name: Get Rid of Comment Websites
*/
function my_custom_comment_fields( $fields ){
  if(isset($fields['url']))
    unset($fields['url']);
  return $fields;
}

add_filter( 'comment_form_default_fields', 'my_custom_comment_fields' );

Normally, I’d say put it into your theme’s functions.php file, but I wouldn’t recommend doing that for a theme that could update like Twenty Ten. This way will let you add this functionality as a plugin which can be disabled.