Automatically approve comments for people with more than 5 comments approved already

comment_auto_approval.php

<?php
function filter_handler( $approved , $commentdata ) {

	// get the comment author name and email and check how many comments that person has approved.
	global $wpdb;
	$author = $commentdata[ 'comment_author' ];
	$email = $commentdata[ 'comment_author_email' ];
	$comments_approved = $wpdb->get_var( "SELECT COUNT(comment_approved) FROM $wpdb->comments WHERE comment_author = '$author' AND comment_author_email = '$email' and comment_approved = '1' LIMIT 1" );

	// if the author already has more than 5 comments approved, set this to approved, otherwise set as pending
	if ( 5 < $comments_approved ) {
		$approved = 1;
	}
	else {
		$approved = 0;
	}

	// return the approved value
	return $approved;

}

add_filter( 'pre_comment_approved' , 'filter_handler' , '99', 2 );
?>

The DB query should probably be prepared - although it's based on WP Core which doesn't use prepare and I don't think it can be exploited (you can inject bad stuff but I couldn't make it break out of the quotes).

Still, if I was using this in a plugin or production, I'd run it through $wpdb-prepare....