You can read more technical details on my christmas hoax writeup page but Perl was used for both the front-end CGI and back-end image generator - the excellent GD.pm module was key for the later.
There was some tweeks between Halloween and Christmas/2004 so that the front-end could run under mod_perl (rather than as a CGI) which has the desired effect and using ApacheBench, I measured the five time increase in peak connection rate - hey, I got Slashdotted 4 times (starting in 2002) which is one heck of a stress test! ;-)
Media wasn't too happy about the hoax and therefore took a few swipes at me - check out my media commentary/correction page and then form your OWN opinion ...