Pros
You will gain valuable work experience, build your portfolio, and be encouraged to learn more about your field. The structure will make you feel like you are a valuable, contributing member as long as you do your work. There is a ceative work environment, a lot of social perks, and you're encouraged to be friends with co-workers. You will also get exposure to a variety of clients and fields.
Cons
Inadequate compensation. Must be able to handle criticism, ridicule, and being made fun of on a vareity of levels. Inadequate compensation. Risk of being "on the outs" if you don't like to party or attend social company gatherings. Inadequate compensation. Expect everyone in the company to know everything about you. Also, there is inadequate compensation.