Pros
Big company, Ok health benefits, the illusion of job security.
Cons
Really frugal (cheap) company, no snacks, employees are required to work on old/outdated computer equipment (lots of developers still forced to work on Windows XP), and managers don't seem to appreciate your input or innovations. I actually applied the Joel Test to the area I worked at within IBM, and found that they failed miserably. If you're a Software Engineer, you'll most likely find yourself working with outdated technologies and programming frameworks mandated by non-technical executives. And if you haven't heard, IBM is laying off people left and right at this time, with the possibility of more layoffs coming towards the end of this year. Definitely not the best company to be at right now.