Pros
IBM has a very good benefits package including but not limited to Medical, Dental, Vision, 401K, ability to buy company stock, and more. The size and reputation of the company also adds a lot of value in certain ways. Since the company is so big, there are tons of opportunities available to you all over the world. They have a lot of professional development trainings and courses that you can partake in to help get yourself ahead of the game.
Cons
As an aquired IBMer, there is a lot of confusion that has been going on with the employees. The aquisition process has been very shaky. We were officially acquired a few months ago yet a majority of us still haven't been issued IBM laptops (which we were told we were going to be issued). Our entire pay day schedule changed which was annoying at first. In addition, the fact that it's such a large company, it is much harder to talk to someone within the company.