Pros
IBM is a good place to work. They are very flexible with your work schedule which is nice. In the decades I've been here I've never been bored, always lots to do. People I work with are great for the most part.
Cons
Most of the time we're understaffed, way too much to do. Salary is sub-par, and the longer you are here the lower your pay vs the rest of the industry. Tons of hierarchy and bureaucracy, can be frustrating at times. They advertise that since they are so big they have lots of opportunities for you to move around and do different things, but if you are good at what you do then forget about being able to shift positions, they want to keep you right where you are. This can be a pro or con, depends on your desired career path.