Pros
I have found IBM a great place to work. I've been here 8 years now and have had great professional (technical) and personal growth in that time. I have been able to move around teams to find the right fit, each time learning new things that have made me a better engineer. I have (most of the time!) felt supported to try new things, safe in the knowledge that if it failed that it is the cost of innovation. There is also a great work/life balance. Of course there is as much work there as you want and I have spent many evenings working late when I felt it was important to do so - never at the insistence of a manager or colleague. At the same time, when I needed support for my personal life (children, illness etc.) it was always forthcoming along with compassion and a human touch.
Cons
It is a big ship, very slow to turn. The internal bureaucracy can be frustrating, and communicating across teams can be little slow/difficult. The pros outweigh the cons in my experience YMMV!