Pros
I have been consistently impressed with the way employees internalize and act on the corporate values at LinkedIn. It is so rare to hear people integrate discussions about the values into everyday conversation, but here it is what everyone lives and breathes. It's a growing, good-sized company that still acts like a start-up (in a good way).
Cons
Decisions at LinkedIn are driven by influence, so it's extremely important to know the right people. That can be a challenge for new employees who need clear processes, because so much is shared by word-of-mouth. It can be daunting because it's not often clear who is responsible for what. Luckily, virtually everyone is approachable and responsive. The positive aspect to the flat organizational structure is that it's easy to implement changes quickly.