404 error handler

A long time ago, we reorganized our website in such a way that all the old URLs that had been indexed in search engines and immortalized in e-mails and blog posts were suddenly nonfunctional. I considered using something like mod_rewrite to redirect the old traffic to the new URLs, but this would be problematic for some URLs (like the URLs into our forum).

Now, this isn't rocket science, but I came up with a way to have my cake and eat it too. I set up an ErrorDocument handler called 404.php that was a script that can redirect people based on their incoming URLs, Referrers, etc:

<?php                                                                          
# Useful _SERVER variables:
# REDIRECT_URL - original URL of request
# REQUEST_URI  - original URI of request?

$map = array(
    "/old/url/path" => "http://www.domain.com/new/path/"
);
if ( $map[$_SERVER['REQUEST_URI']] ) # if the request is in the map
{
    header("HTTP/1.0 302 Moved");
    header("Location: ".$map[$_SERVER['REQUEST_URI']]);
    exit();
}
if ( substr($_SERVER['REQUEST_URI'], 0, 9) == "/download" )                    
{
    header("HTTP/1.0 302 Moved");
    header("Location: http://www.domain.com/new/download/path/");
    exit();
}
?>

I checked our access logs for 404 errors a few times a week and added into the map the most common hits.
Well, I thought it was clever...