Pros
Digitas is pretty good at hiring smart people. With only one exception, everyone I have worked with was good at their job! The culture is great - non competitive, but people take their work seriously. Things like community service day are really well executed, fun, and meaningful. As a recent college grad I learned a lot quickly about how to navigate and get stuff done in a large organization. The GDP goals program makes sure that managers have to spend time with you, which is good. Diversity seems to be a priority, with women and minorities in highly visible leadership and management positions. This isn't a 50s style "boys club" mad. ave ad agency. But I can't emphasize this enough: people, really good people.
Cons
However, the rigid 6 month promotion / raise cycle makes it hard to advance quickly. If you miss your promotion, but would have been ready in a month, you get screwed. Also: Long hours. Really long hours.