Pros
The company has a lot of talented people -- the Software Group consists largely of acquired companies, and the people bring with them a passion for the products they work on. My complaints about IBM have nothing to do with the quality of its employees. Work schedule is fairly flexible and benefits are decent. Office space in Littleton, MA was reasonably nice, though all cubes.
Cons
IBM seems to have a "resource action" (massive layoff) every year, regardless of whether or not the company is profitable. Additionally, their review process has "quotas" for each rating, meaning that even the very solid performers can go for years without getting a raise, and good people are "set up" with poor reviews only to be cut in the next round of layoffs. Though that never happened to me, I saw it happen repeatedly to co-workers: good, talented people. Things aren't any better for the people left behind after all of these cuts -- people who leave (whether via attrition or layoffs) are not replaced, and projects are under-resourced and people overworked. And you have to watch as good people are given their walking papers, wondering when it'll be you. IBM also talks about "work-life integration" as opposed to "work-life balance," implying flexibility in work schedules, when what it really means is having to do phone meetings at 6:00 AM or 9:00 PM, if working with people in radically different time zones, which seems to be the rule rather than the exception as IBM offshores more and more of its US jobs. Overall, it creates a toxic environment that crushes the spirit out of people who have a lot to give.