Pros
IBM is so focused on learning. They offer hundreds of thousands of free courses on Udemy and O'Reilly. Managers will also get you setup with courses with live instructors teaching. Everyone at the office I work at is set on finding a project for you. Until you find one, just soak all the knowledge that you can, it's offered to you and encouraged. While you are "on the bench" (not on a project) and most projects, everyone is extremely flexible. Everyone has a life outside of work and mostly everyone knows that. I think this is a fantastic environment and place to work. I'm proud to be an IBMer.
Cons
I can't really think of one. However, I do want to talk about 1 con that I have seen a lot. IBM does require on some projects that you work 45 hours week. There is a reason for this. Remember all of that free education you received, that certification you didn't pay for that will follow you anywhere you go, the paychecks you received during this, when all you have done at this point is cost the company money? This is where you make up for it. Now that you are generating income for IBM, that extra hour a day is your repayment. 1000% Worth it if you ask me. I would have spent thousands of dollars on the courses, live classes, and certifications I have received, if it wasn't for IBM investing in me.