Pros
It's nice to be in an environment where marketing decisions are based on actual program performance data rather than someone's instinct or endless rounds of focus groups. The amount of data we can access about our marketing programs is mind-blowing. Every team has dedicated web developers who can build any kind of web analytics tool that you can imagine as long as you show its value. Co-workers are generally very smart and helpful. The growth is happening fast so there are decent oppys to advance your career if you do a good job. Next year we're getting a new building with a bball court and gym and running track.
Cons
The pace of change is unbelievable. The turnaround times are really short and it can be high pressure. It's something that takes getting used to if you come from a slower-moving or larger company. The learning curve was steep for me and the first few months were seriously intense but if you can adapt its a really good place to work.