Pros
You get firs hand information, support and training from Facebook, Twitter and Google. It's a diverse environment that connects you everyday to people from all around the world. You get the chance be involved in global campaigns and get to learn a little of how other markets work. Big budget to work with. Clients in some markets are very nice and good to work with. Gets you insight about how one of the biggest brand in the world does marketing. Steep learning curve if you are proactive and care about career development
Cons
Long work hours. Salary is not based on your actual work or performance but rather on the years you've been working for the agency or the circumstances of the moment when you where hired. In order to deliver results you might have to compensate for the other people's lack of professionalism. They constantly pressure the team to do more with less. Some campaigns are poorly planned and the executions of others often get affected by the constant really cramped deadlines.