Pros
Lab is quiet and remote. Flexible working hours, working from home. IBM's external recognition is still somewhat good, so it has some value on a resume. If you are starting fresh from school, it can be a good place to learn and gain some experience. Decent benefits. Many locations around the world for relocation.
Cons
A lot. Low pay, no transparency at all about company decisions, bureaucracy at its best. It has to be the workplace in the world with most meetings per capita, where most of the workforce career goal is to to reach some (people or project) management position. The quality of the technical workforce as been aggressively depreciating with the top performers regularly leaving as they cannot stand the management hypocrisy and all the politics anymore. As a result, IBM is today one of the last places where recent grads and tech workers apply for jobs in the Bay Area. Most of the fresh-out-of-school hires come from San Jose State Univ, as IBM cannot capture the interest of students from top schools. This then reflects in the lower quality of work and software development practices. Definitely not a place to stay long after you get your first 2-3 years of experience, unless your goal is to be in management.