Facebook uses the LAMP stack, so if you want to get a career with them you're going to want to focus on that. In addition they often have C++ and/or Java listed in their requirements as well.
One of the postings includes the following requirements:
- Expertise with C++ and/or Java
- Knowledge of Perl or PHP or Python
- Knowledge of relational databases and SQL, preferably MySQL and Oracle
Another:
- Expertise in PHP, JavaScript, and
CSS.
Another:
- Knowledge of Perl or PHP or Python
- Knowledge of relational databases and
- SQL, preferably MySQL Knowledge of
- web technologies: XHTML, JavaScript
Experience with C, C++ a plus
Source
http://www.facebook.com/careers/#!/careers/department.php?dept=engineering
Also, do any other social networking sites use the same language?
Some other companys that use PHP/LAMP Stack:
- DeviantArt (more focused on art)
- Twitter (for Front-End development)
- Google+
