I think LadyAnna pretty much said it. I use OOP because the organizational benifit far outweighs any sort of 'convenience' that all-out procedural can offer. Now saying that, I'm not an OOP-nazi. I program mainly in C++, not Java, so I do switch between global functions/variables and class-scoped functions/variables (or members/methods). In all honesty, I'm a hobbyist programmer, and I've never really taken any formal classes (except for High School Computer Science, which is a friggin' joke), so my advice isn't part of the 'industrial standard'.
If you just want some examples of OOP to browse around, you're likely to find them in projects using an MVC architecture, such as CakePHP (which deals with more than PHP, though). Other things you might want to look at are the Zend Framework, or CodeIgniter, or maybe some of the big CMSes, like Joomla or Drupal (can't say if they stuck with procedural or OOP most of the time).
Heck, I'll put my usual plug in. You can browse around the
source for Thacmus, my CMS project. I've designed with things I've learned from programming namely in C++, which also consists of stuff I learned (to love and hate) with GML, VisualBasic, JavaScript, etc.
My story: [Kinda long...]
I started learning PHP a while ago, after I had been using Game Maker (thusly GML), meaning I had no experience with OOP whatsoever. I was procedural all the way, and scoffed at people who had to use classes to organize their code. After half a year of just screwing around with PHP, not really doing much, I left it and went back to mainly using GML. I later got tired of GML, and finally decided to learn C++ (for the third time). That time, after experience with GML and PHP, I could grasp the syntax of C++ a little more easily. I started to program crap, and then decided to start writing a game with C++, and for that matter, a game engine, just for learning experience.
I started out trying to make it as close to GML as possible, meaning I used classes sparsely, and only then for polymorphism and grouped variables. I hardly used normal functions.
After a while, I realized why I had stopped using GM, and stopped trying to imitate it, and went off on my own designing things how I liked.
It gradually evolved, and I frequently tore it apart, refactored it, redesigned, left it for a couple of months or so, came back, did the same thing, and so on, just so I could get around to working on a MegaMan X fan game I wanted to do. Needless to say, I have quite a bit of A.D.D. (normal for a programmer), and switched back to PHP for a while, since I was helping out with my school band's website.
When I began to compare the way I coded with PHP before and the way I coded with C++, I realized that using OOP with PHP is actually a good thing to do. I noticed this when I was designing the framework for the band's site, and I noticed how repetitive certain tasks were. I also remembered how much of a pain in the ass it was to write MySQL code with PHP (I had written some bus signup software just for the hell of it, and it was truly a pain), so I thought to myself, "What's the best way?" So I programmed some stuff in procedural like I used to, looked for patterns, started simplifying the patterns, encapsulating the patterns, generalizing them, abstracting them, yadda yadda yadda.
Yeah, I was kinda windy there, but you get the point.
EDIT: Way too windy.