Pros
You will be working with some of the smartest and most driven people in technology. If you find the right group who is passionate, it can be an amazing experience. They have the money to do forward thinking research which allows you to spend time doing the work, not looking for funding. The workplace is flexible and you are allowed a great amount of autonomy.
Cons
It is too big. It is impossible to get anything done and there is no central clearinghouse for paperwork issues. People rarely know the person 2 rows away - it's not a very social culture. It's difficult to get anything done without a committee and everyone is allowed to and encouraged to have an opinion, whether or not they have the background to understand the issue. It's hyper competitive and instead of working together for the better good, sometimes the company shoots itself in the foot by having small groups all working towards common goals separately instead of together.