Pros
There is a huge potential for impact. If you have a great idea and can convince others to join you, there is very little process stopping you from building awesome new stuff and shipping it to the world. Practically everyone I know, and everyone I meet, has used the software that I've written.
The company culture and values are amazing and everyone is totally on board with them. There is no politics or infighting and everyone is really on the same team trying to make facebook better.
Facebookers are extremely smart people and super passionate about their work. We aren't afraid to take on new risks or big challenges.
The technology stack is mind boggling. When I started at facebook a few years ago, every day I learned something that made my jaw drop. The same thing still happens to me on a regular basis years later.
Mark and Sheryl make a great pair of leaders that I have the utmost confidence in.
There are excellent learning and development programs/opportunities that help you progress in your career.
The benefits are obviously awesome too.
Cons
We don't really do april fools jokes which is kind of a bummer.
There are some dragons in the code base, and they breath fire.