Pros
You'll meet a lot of great people, both within the company and clients. ZI tends to work with the most well-known and well-connected people. It's a very family atmosphere. Career development opportunities are tremendous.
Cons
It's intense. IMHO, that's a good thing. Some folks starting in the competitive world may not understand this. While I think some approaches could be reconsidered, overall, the real world requires a competitive edge and a driven staff. This creates pressure that people starting in the industry may not fully understand until they've been in it a while.