Addressing both replies: Facebook continues to have perhaps the highest ratio of users (choose a metric if you wish) to engineers, quite possibly by a large margin. I believe that's a good proxy for responsibility.
reddit, pinterest, and craigslist come to mind as probably having a higher ratio. Instagram too, before Facebook bought them. Edit: And OMGPOP before Zynga bought them.
The most recent estimate I saw was 1.3m users/engineer and steadily climbing. And if we take active users, the gap is even greater. And none of those other companies would enable an engineer's work to get in front of 100s of millons of users.
With 900m users, a ratio of 1.3m user/engineer would mean only 692 of their 3500 employees are engineers. That seems low to me. I'm also having a hard time imagining their ratio is growing, their monthly percentage growth has been steadily slowing down, I doubt their hiring has been slowing even further.
