Pros
There is a good policy on home-office work, this means you can work in your house whenever you feel it is necessary, this to avoid distractions of usual office work. There's a strong knowledge on computer science among your co-workers.
Cons
IBM is in a very deep crisis worldwide and this fact reflects on IBM Research. I have seen many problems with budgets. This is the place where you don't want to go because they won't invest nothing on employee training, you will get tired of never ending conference-calls and inner "technical" presentations that don't lead to nothing. IBM has very few research projects with the industry so you won't experience real life research. Since IBM tries to do research on any field it has not a clear leadership on areas rather than computer science. If you have another field of expertise you won't grow here. IBM Research has cut annual benefits on salaries due to crisis inside IBM. Even if you are a Director in IBM you won't ever fly on business and you will always stay on budget hotels. You would think that if you come to work in IBM Research you'll have a really nice computer, forget it!!! They will give you a refurbished T-420 lenovo. If you look on to any search browser for: ibm crisis, you will know what I'm talking about.