Pros
Generally this is a good place to work. Most first line and second line managers are also technical people, so most of the time they understand and appreciate individual researcher's work. Working hours are very flexible. Researchers are supposed to work 40 hours per week, however nobody keeps track of working hours. So you'll be good as long as you do a satisfactory job. Researchers also have some flexibility in choosing which projects to work on and coming up with their own projects. Collaborations between different groups are quite common and are encouraged.
Cons
IBM Research (Watson) is at a very expensively location. Living costs are among the highest in the nation. Salary for entry level researchers are reasonable, however the growth potential is very limited. Bonus (variable pay) has been a joke recently although IBM stocks are strong.