Pros
Driven Culture, very few politics, lots of perks, Facebook tries to maintain the start up culter and allow massive amounts of freedom to shape your own job and your own work. The review system can be the best getting honest peer review feedback that makes your work better.
Cons
sometimes too demanding, no life half of work life balance. Its a driven and competitive culture the person sitting next to you doing 12 hours days and weekends will get ahead faster. The bar is high the demands are high and there are no rewards for failure. Doing the same thing this year that you did last year is considered failure. Its not a good place for folks with lives and kids out side of work. The review system can be the worst with nepotistic back scratching in an echo chamber.