Well it has been a long time coming, but the PHP community has finally announced the end of life for PHP 4:

"PHP 4 end of life announcement" - http://www.php.net/index.php#2007-07-13-1

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Updated 2021 : note that the above post was originally published in 2007, but is left here for archival purposes. The external link is now dead so I have unlinked it.