Well, objects aren't really fully supported by PHP yet. PHP has made strides to support it, and you can use Object Oriented Programming (OOP) in PHP. It has its limits, and is superseeded in other languages that are OOP languages.
From what I've used, PHP 4 really limits OOP, and PHP 5 opens up the doors to it. I can't say that I've personally been limited by PHPs Object handeling, and I know of 1 application that uses OOP and is fairly successful (PHP Support Tickets).
~Brett