The second link in this blog post does not appear to be the complete youtubedown, but instead a truncated version with a .cgi extension.
They are two different programs.
Faugh, I missed the bit about bookmarklet, which probably explains things.
By reading the source code of the script one can relive the horrid Descensus ad Inferos jwz has been through.
When I try to download the perl script to my machine using wget I get a 403 Forbidden error... ?