Pros
You get an opportunity to work on some incredible, award-winning projects. The culture there forces you to be constantly learning because you are asked time and time again to do things no one has done before. The design team there is top notch and are very good about sharing knowledge.
Cons
Prepare to give it everything you have. Nights, weekends, vacations... Prepare to not make a lot of money. Prepare to have designers doing your PR, your engineering, your management. They really only hire designers so designers do all the work, even the non-design work.