What every big company uses PHP for- To avoid lawsuits & also the fact that is it open source. Think of Android which got Google a lawsuit filed against them just for using java which somehow Oracle bought with their power. The open-source languages & technologies like C, C++, PHP, PERL among others appear so out of touch but when you use it with other freely available languages & databases like mysql, xml, javascript, ajax, json they become a power-house which even the top technologies like JAVA & .NET cannot measure upto
Facebook uses PHP 5.
Because it works so well with PHP and it's fast.
Php hosting is a popular scripting language in which produces dynamic web pages. An example of a dynamic web page is Facebook. Facebook needs php hosting as it has a login page. Shopping pages are also php hosted.
PHP
php
PHP, HTML and Occasionally Flash. Using a SQL style database if using Facebooks Database.
facebook definatly runs on php (as you can tell by going to www.facebook.com/home.php). Also when you apply for a job to the company mysql knowledge is a must. However as for the platform it runs on that is difficult to say for sure, however i would imagine them to be using a classical LAMP setup (Linux Apache MySQL and PHP) as is very common with php/mySQL sites.
PHP, Html
You search for the application maker and the follow the steps their. Facebook allows you to develop application in php or asp.net and then integrate with facebook.
There are millions of websites that use PHP, some notable ones are Facebook, Digg, Wikipedia and many more.
It supports websites made on php but not coding in php. There are workarounds for coding in PHP using Android.
Many jobs can use PHP, a lot of gaming companies around the United States are looking for PHP programmers. Zynga may or may not still be looking for it, and Facebook as well.