Despite the changes in copy semantics from PHP4 to PHP5, most code written for PHP4 runs fine as PHP5. If changes are necessary, they are very minor since PHP5 mostly adds new capabilities (apart from the pass-by-reference stuff). If the coder was using "&" before in his PHP4 code, then it will work fine without changes in PHP5. The bigger question for me is whether the excellent www.cakePHP.org framework will continue to support PHP4 now it's deprecated.