Pros
Some of the people are quite intelligent and don't have the cutthroat mentality. They don't last long - they make the rational decision and leave to find a place where you actually get paid and treated like a human being.
Cons
Idiotic management that likes to throw out vague meaningless catchwords like "adding value" or "team spirit". Pay freezes due to the economy (mainly for non-management of course). Co-workers that backstab you and try to steal your ideas. Illogical situations like a creative director pretending he knows more than the analytics staff in regards to data. Unqualified people attaining leadership roles through sheer horse-trading politics. Insane hours where you are expected to work until you drop for 1/10 of the pay of an investment banker. An atmosphere akin to high school where who you know is more important than what you can do. Layoffs when your client realizes the creatives, analyses, and Rapp management are garbage.