Pros
Far and away the best job, best boss, and best coworkers I have ever known. Valiant, much as its name would suggest, prides itself on a noble need to do right. These guys do right by each other, and they do right by the client. I have never seen such a unified work ethic at an employer. Professionalism and excellence are mandated in all transactions, but it doesn't come from a fear of scolding or punishment. It comes from a fear of disappointing your colleagues, and yourself. You are expected to take ownership of your tasks and your mistakes, and grow from them. I've learned so much about personal accountability from my experience at Valiant.
If you don't want to laugh every day, this isn't the place for you. You will be subjected to the funniest, smartest, weirdest people in the world. Senior management vets for personality as much as skill, and this has resulted in the geek frat of your dreams. I have met some of the most important people in my life at Valiant - though I have moved on to a different role, I still hear from at least one former coworker every day.
Cons
Change is encouraged - you may be moved to a different wing of the office, or may be offered the opportunity to become embedded at a client. If you're expecting to sit at the same desk for 5 years, you'd better Gorilla Glue your feet to the floor. If change exhilarates you, know that your fresh ideas will be welcome.