~4000 for Twitter (although I vaguely recall a culling recently, not sure how many they let go).

I'm curious what does these 4000 employees do at Twitter ? let's say half of them are engineers, what are these 2000 engineers working on ? Twitter is mostly CRUD and messaging.

This is fitting here: http://danluu.com/sounds-easy/

Analytics, Reporting, Ad management and Biding platform, Fraud detection, and way more.

This basic CRUD app is just user-facing thing, and now remember that they are making money not because of you, but because of publishers. This is where main functionality is.

There'd be more than the consumer-facing systems. Whether they require 4000 people to run it all is another question, but without a deeper look into what's running, it would be hard to surmise.

You do realize how much engineering goes into Github, right? I can't even imagine the number of DDoS they have to deal with on a weekly basis. Not to mention all the hardware they have to move around; any system with that many hard drives has got to be extremely dynamic.

50 people seem enough to deal with them full time no?

Why?