Pros
An entrepreneurial environment where you are given a lot of opportunity to grow professionally. You'll do very well if you're ambitious, not afraid to ask questions, and live by a personal credo similar to "ask for forgiveness, not for permission." People are friendly and genuinely nice and managers make the effort to understand your needs and help you develop your skills. Transparent and open, management follows the culture by example. They seem to actually care about the work environment and are pretty active about fixing and preventing problems. This is not a hacker-style startup; the company is very mature despite their size. You are given opportunities to grow and succeed, but this is not the place if you need hand-holding or be given step-by-step instructions.
Cons
Not a lot of cons save the occasional growing pains associated with young, growing companies.