FB: Hard Problems and Fun People
Pros
It's a social networking company so it pre-selects for social people. Most of my coworkers want to be friends in addition to colleagues. The scale is amazing: it's exciting but also humbling to sit in a room and talk about how 1B will use our product. With that scale comes the requirement for precision in algorithms, data structures and code clarity that I've never experienced before.
Cons
Being very data-driven can push out more sentiment-based projects and sometimes puts too much of a burden on teams to identify exactly the right metric to optimize for. Tooling for developers is improving but with such a large codebase and so many developers, creating a branch, making a change and building can take a long time. This is especially true on mobile.