Pros
The pride of working for Big Blue, recognition everywhere. It opens doors for me if I want to move on to something else. Great worklife balance and understanding managers. I am allowed freely take time off when I need to, no questions asked. I also get to work with some really brillant people (and of course, some pretty dim ones too) in the cutting edge of technology. There are also a lot of opportunities to move across jobs and functions, which is great because you get to try out different jobs without losing seniority. There is also a very good training structure where you can easily take courses you are interested in.
Cons
I did not like the huge bureacracy that came with a large company. Lots of red tape and also lots of politics. The waves of layoffs I experienced (even though I was not affected) was demoralising, but I guess it's the general economic situation at that time. And being large and old, there are a lot of deadwoods around, people that dont do much work but draw a high pay. Paywise, it was alright but not great. Bonuses were neglible.