Pros
Very progressive in conducting business and cultyre. The company encourages feedback, so management is not only receptive, but also very responsive in changing if it is warranted. The company breeds entrepreneurs and autonomy. Leadership is as transparent as I've seen any business be (big and small), and really takes care of its people first. I've worked at and for dozens of companies and clients who are "progressive", "exciting", "innovative", and no one compares to FB.
Cons
There are so many opportunities, it's hard to know what your career path might be. It's an extremely competitive company based on the caliber of talent at the company. Life/work balance is encouraged and supported, however it's up to the Employee to make it happen...and if others don't, it's hard to keep up if you aren't as efficient.