Pros
If you are a Ph.D. and want to work in the industry but still be in touch with the academic work, IBM Research is one of the few places that can provide that opportunity. As a research staff member (typically only Ph.D.s are hired), you will be measured based on three things: 1. your project work and how much it contributed to the company in terms of cost savings, revenue impact, or other qualitative impact, or technological advances if you are lucky enough to be working on such things 2. patents you file, 3. papers you publish. Since IBM is a global company, the projects can come from many different industries and many different locations in the world. The Research division enjoys high respect within the company but much more so outside the company.
Cons
IBM's obsession with pleasing the Wall Street brings about a short sighted view to its research policy and hence impacts its Research negatively. All parts of IBM unfortunately scramble to meet short term financial objectives and Research is very often called for help, which takes researchers away from their primary roles of inventing and innovating game changing technologies and methods. By definition, research means investing time and money in high risk high reward problems. For instance, Watson was developed over quite a few years with dozens of people involved. That is what it takes to create serious technologies. Watson team had the few lucky researchers. Unfortunately, many researchers find themselves in a situation where they are asked to help the other parts of IBM improve their bottom line. Since other parts of IBM provide research its funding, they have a lot of influence on defining research projects and therefore how researchers spend their time. Since they are hard pressed to meet their financial objectives, they tend to define projects that help their short term financial goals. Such projects are almost always less innovative and tend to have marginal value for the company. IBM researchers are very capable people. IBM hires the very best to its Research. However, under so much pressure to help IBM's bottom line and do it fast, it is hard for researchers to come up with earth shaking innovations, though they would be perfectly capable to do so if they were given some breathing room. There are still quite a few researchers who still get to work on really promising things but their numbers are quite small.