Pros
The PEOPLE - very motivated, interesting, educated people. You get to work with the brightest minds in the GIS field from all over the world. Lots of challenging projects, and the abiltiy to move to different projects. ESRI gives $3000/year education benefits to everyone, plus they give several full scholarships to Univ. of Redlands every year through a competition.
Cons
Can be chaotic. Managers often change the goals in the middle of projects. You may have to work a lot of overtime, so it's no place for slackers. Communication between departments is lacking. Sometimes you find out that another department is doing exactly the same project you are doing. Each department acts like an independent company, sometimes competing with each other.