There are blog posts that you can write without doing any prior work (he says, looking meaningfully at himself in the mirror), and then there are blog posts that require real work. This very interesting post about how the Facebook development organization operates is in the latter category. Instead of pointlessly summarizing the author's findings, compiled from sources who know Facebook from the inside, I'll add a few reactions:
If, as reported, the development team comprises about a quarter of the company's employees (and operations another quarter), that's an unusually high ratio for any tech vendor, whether or not it's in the software-as-a-service (SaaS) business. At salesforce.com, R&D comprises 15% of the company, which is high for the tech industry. Facebook's 25% R&D is staggeringly high.
Even though Facebook regularly confuses the heck out of the people with changes to security features, the company does pilot features before shipping them.
Facebook developers bear a lot of responsibility for their own code, across many dimensions of quality (design, testing, justification, etc.).
The ops team has a more gradual approach to deploying new code than it might appear.