Export WordPress Comments as Excel file. Uses PHPExcel, http://phpexcel.codeplex.com/. Place this file in the root of the WordPress installation. TODO: convert to plugin.

comments-2-excel.php

<?php
# Load slim WP
define( 'WP_USE_THEMES', false );
require( './wp-load.php' );

# http://phpexcel.codeplex.com/
require_once dirname(__FILE__) . '/Classes/PHPExcel.php';

global $wpdb;
$query = "SELECT * FROM $wpdb->comments 
    WHERE 1 = 1 
    AND ( comment_approved = '1' OR comment_approved = '0' ) 
    ORDER BY comment_ID DESC";

$error = "Error: the query failed...
    <pre style='width:700px;word-wrap:break-word;white-space:normal;'>$query</pre>";

$result = $wpdb->get_results( $query, ARRAY_A ) or wp_die( $error );

$objPHPExcel = new PHPExcel(); 
$objPHPExcel->getProperties()
		->setCreator("user")
    		->setLastModifiedBy("user")
		->setTitle("Office 2007 XLSX Test Document")
		->setSubject("Office 2007 XLSX Test Document")
		->setDescription("Test document for Office 2007 XLSX, generated using PHP classes.")
		->setKeywords("office 2007 openxml php")
		->setCategory("Test result file");

// Set the active Excel worksheet to sheet 0
$objPHPExcel->setActiveSheetIndex(0); 

// Initialise the Excel row number
$rowCount = 0; 

// Sheet cells
$cell_definition = array(
	'A' => 'comment_ID',
	'B' => 'comment_post_ID',
	'C' => 'comment_author',
	'D' => 'comment_author_email',
	'E' => 'comment_author_url',
	'F' => 'comment_author_IP',
	'G' => 'comment_date',
	'H' => 'comment_date_gmt',
	'I' => 'comment_content',
	'J' => 'comment_karma',
	'K' => 'comment_approved',
	'L' => 'comment_agent',
	'M' => 'comment_type',
	'N' => 'comment_parent',
	'O' => 'user_id'
);

// Build headers
foreach( $cell_definition as $column => $value )
	$objPHPExcel->getActiveSheet()->setCellValue( "{$column}1", $value ); 

// Build cells
while( $rowCount < count($result) ){ 
	$cell = $rowCount + 2;
	foreach( $cell_definition as $column => $value )
		$objPHPExcel->getActiveSheet()->setCellValue($column.$cell, $result[$rowCount][$value]); 
		
    $rowCount++; 
} 
header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
header('Content-Disposition: attachment;filename="01simple.xlsx"');
header('Cache-Control: max-age=0');

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel2007');
$objWriter->save('php://output');
exit;