Pros
In my experience, IBM does a great job of career management. My managers have always been heavily invested advancing my career, giving me opportunities to shine in front of executives. And they've always had very frank and open discussions about my career goals and how to achieve them at the company. Another advantage is that just about any job you can conceive of exists within IBM and you can find it and position yourself to get it - if that's what you want. Finally, the company is so invested across all technology areas that you can always move to some new, exciting area if you want, or need, to.
Cons
Benefits are bare-bones and employee contributions are increasing every year. Constant "resource actions" force remaining employees to do more, with less. And in a company of 370K+ employees, it's hard to feel like your individual contribution really matters.