Pros
Excellent employee perks and onsite services such as banking, drycleaning, daycare. If young and just starting your career, there is definitely a lot of areas for horizontal movement within the company.
Cons
Very hierarchical - many in management positions refuse to correspond with those in positions they deem at a lower level then themselves. It takes several follow-up attempts to get answers from co-workers and other departments - most of the work day is filled with continuously following up with people when they do not respond. A good portion of those in management positions got there by just being with the company in it's infancy and as such, they do not have well developed management or people skills. They tend to low ball the compensation offers. Everyone I've spoken with has been told during the interview process that they are significantly overpaid, that the company doesn't pay that high for that particular position or that there isn;t enough money in the budget. They will cite the many perks and benefits, but keep in mind these onsite benefits are really so that you don't have a reason to leave the building during the day (hint: so you can work longer hours). Parking is horrible, although there is a shuttle bus service in the front of the building it only runs during certain hours. This is mostly a problem during inclement weather.