Pros
Great people to work with. Expert engineers are always available throughout the company and great network in place to reach out to anyone. Matrix organization is followed, so you can make career moves in different directions. Work is most of the time challenging, once you gain the trust of senior engineers, you can start running your own little projects but they are always there to review, check and help you if you need.
Cons
Depending on the office size and client base, career development can be a struggle. If there are too many project managers and not enough junior level engineers doing the work, you can stay in the same position for a while. No clear advancement structure. The "you can be anything you want to be" attitude can stall your advancement if you do not know what you want out of your career and you do not have a close relationship with a senior level person to help you understand and guide. You really need to speak up, otherwise I have seen many quit because they can not advance - especially when there is no strong leadership in the group.