From an interview with someone on the engineering team (sounds like). Lots of interesting if unsurprising stuff about privacy, and this:
Rumpus: So tell me about the engineers.
Employee: Theyâ€™re weird, and smart as balls. For example, this guy right now is single-handedly rewriting, essentially, the entire site. Our site is coded, Iâ€™d say, 90% in PHP. All the front end â€” everything you see â€” is generated via a language called PHP. He is creating HPHP, Hyper-PHP, which means heâ€™s literally rewriting the entire language. Thereâ€™s this distinction in coding between a scripted language and a compiled language. PHP is an example of a scripted language. The computer or browser reads the program like a script, from top to bottom, and executes it in that order: anything you declare at the bottom cannot be referenced at the top. But with a compiled language, the program you write is compiled into an executable file. It doesnâ€™t have to read the program from beginning to end in order to execute commands. Itâ€™s much faster that way. So this engineer is converting the site from one that runs on a scripted language to one that runs on a compiled language. However, if you went to go talk to him about basketball, you would probably have the most awkward conversation youâ€™d have with a human being in your entire life. You just canâ€™t talk to these people on a normal level. If you wanted to talk about basketball, talk about graph theory. Then heâ€™d get it. And thereâ€™s a lot of people like that. But by golly, they can do their jobs.