Pros
Pension. There really isn't any other pro in working for IBM, except possibly that it's easy to hide yourself if you are a low achiever. Even then - that might not last long.
Cons
Everything else. IBM has little care for their products and their employees. As a result they sell mediocre products supported by a dissatisfied work force. Their strategy is one size fits all - as such, strategical decisions are not made taking into accounts product value, product investment, existing resources, and investment efficiency. At the next round of cuts, everyone gets the same percentage of heads chopped off . A hire freeze applies whether a product is yielding $7M/year per developer, or $0.1M. The next killer product is staffed uniformely stealing heads from every other team - as a result it is designed and built by those heads the other teams could spare.... The former premise, and the work environment, is such that you are forever requested to widen your commitments to the company, with a promise of recognition of career advancement and recognition - somehow they aways fail to materialise. There is a talent retention program, which is interesting because if IBM kept their side of the bargain, they wouldn't need one to start with. It also amounts to: "If you stay, in the long run we'll see if we can do something 'significant' for you"