While specific official and unofficial business practices vary per org or even per team, I feel that overall company culture is actually very strong. At FB, I found that there was a universal culture of (ruthlessly) optimizing for "impact." Obviously what impact was varied with your job and your role but I felt like a key unspoken job responsibility was to help come to a shared understanding of what impact was for your role. Another notable cultural trait was a strong preference for empirical data and a commitment to actually rationalizing conclusions drawn on it. Overall, the culture is what I'd call extremely pragmatic.
Google is very different. It's a much more academic-feeling atmosphere. Everyone understands that the company pays us to do a specific job, but there's a very strong tendency to do "Cool Stuff™" and figure out what the business value is later. Consequently you get a focus on very high quality technical excellent, meticulous and high quality docs and internal systems that are very powerful but perhaps a touch more complex than they need to be ;).
I will say that perhaps some of this is exists only in my head as a result of connecting data points that are actually unrelated. But hey - that's pretty much what culture is anyway so I feel okay sharing my take.
Consider the dead lake effect, the good people will eventually be subjected to sociopaths and will leave, while the sociopaths will stay to fight among themselves.
If you don't know what it is, it is the management theory that you should be actively trying to fire/get leave/layoff your lower performing 10-20% and hiring to replace them.
The false god of this failed religion is that you can measure people's contributions despite cronyism and petty motivations, when the reality is that cronyism and petty motivations dominate.
As even in my 80 person company, you will have radically different experiences depending on the team.