Matt brings up some good points. What might be limiting PHP 5 adoption, could just be the lack of interest in developers. [...] Up until reading his rant, I've lived in a box where everyone I've talked to, used and enjoyed PHP 5 and its vast extensions. Developing in PHP 5.0 was uneventfully, but you learn to appreciate PHP 5 with the core inclusion of PDO with PHP 5.1. PHP 5 is not without annoyances. In the core developers attempts to "better" the language, they made changes that broke code that previously worked.
He looks at a few of the items for debate surrounding the move from PHP4 to PHP5 including the extensions that come bundled with PHP5, solving the register_globals issue, and a brief mention of the Standard PHP Library.