Pros
Really world-class software company, operating at exceptional data, users base and load scale. There are plenty of opportunities to learn and to grow. Lots of really bright people with very different skills and background. Immediate impact of your work on millions of users, adrenaline level is pretty high. Corporate culture is still very strong despite it has eroded somewhat over a few recent years. The focus is on openness and free speech and internally the company is very open and free. Compensation is fairly good, confortable office, very flexible working hours.
Cons
Organizationally and technolgically many things are done very ad hoc. The company didn't handle its scaling very well, it falls behind the pace it grows with. Anyone can come up with an idea (which is good), but often it is unclear what one has to do for the idea to have a chance to become real. Often it is not clear who is responsible for what, who is in charge of making a decision, how plans of various departments match each other. Many processes are inefficient, producing much frustration. It feels like a lack of big ideas, big vision for both products and technology, and this lack feels on all level - from bottom to top.