Pros
I spent many years of my career at IRI. It was basically the first job I had out of school and when I joined in 1987, the company was growing like crazy. I was immediately given as much responsibility as I could handle, worked by butt off, and moved up quickly. I acutally left for a little over six years and returned, which is saying something. My second tenure there was another period of significant career growth -- and I was actually able to shift my career focus from Client Management to Human Resources, a move I remain grateful for.
Cons
The culture changed dramatically several years ago when the company was taken private. What was once a casual, flexible environment became a much more political climate. Part of it was growing pains, I suppose, as the organization began to mature. Part of it was driven by the casting in the "C" suite, in my opinion.