Pros
IBM is a large company with a lot of great people to work with. The IBM community is diverse, with locations around the world with people of all races, creeds, religions and beliefs. With all of this diversity, I think IBM has the ability to do anything it wants. The talent pool seems endless and the opportunities that arise for its employees are there if you are motivated to go after them. Often when you come out of college, you think you know what you want to do, but once you start doing that job, you find that it just doesn't suit you. IBM has many many disciplines that allow you to morph your career should you desire a change.
Cons
It is a large company, and this isn't for everyone. Still, I believe if you are motivated, the large size shouldn't be a problem.