Set your expectations low, really low and plan to move to a different company in a few years
Pros
If you are not ambitious and not passionate about your work, if you don't expect much in terms of professional respect, opportunities, fair compensation and fine with being layed off at any time, this might be a company worth considering.
Cons
IBM internal performance review rules promote meritocracy. You can work very hard, accomplish a great deal and still be given a bad or average performance rating just because you were not visible enough to the right people or simply because it was your time to take one for the team. Most employees I know of have given up on trying to improve anything in the products. People are in "survivor" mode - minimum effort for maximum benefit and don't stick your neck out. A lot of truly talented technical people have either left on their own or were layed off. People that seems to be staying behind are poor souls that are stuck at IBM for some reason, or those who play internal politics well.