Pros
Lots of personal growth/learning opportunities. Good benefits, relatively flexible hours. You'll work with some of the nicest people you'll ever meet.
I've personally experienced multiple promotions and raises in the past couple years, and I feel like the company is doing a better job of compensating people fairly, even though salaries just starting out are on the low side.
This company is still growing rapidly and changing all the time, which can make processes and stability seem non-existent for people who stick around, but the Golden Comm of even one year ago is radically different than what it's trying to be now.
Cons
Overly stressful at times, this company's idea of training is to give you a project and tell you to get started. Whether you like that or not depends on what type of worker you are. It can be extremely frustrating, but if you're independent-minded and catch on quick, it's not too bad because everyone is super supportive. Expectations can be pretty high at times, and the pace you're expected to work at can be ridiculous.
Projects feel sloppy more often than not and messing up in some way seems par for the course. No one holds mistakes against you, since everyone is "learning".
Like any agency, clients are constantly demanding things from you and generally making your life hard. It's an agency, what do you expect? Get in, get some experience, get out and work for a corporation so you can be the bully :)
...So, it's a mixed bag. The "start-up"-like environment here is definitely not for everyone, but as far as agency work goes, I've worked at much worse.