Pros
On the brighter side IBM gives easy work culture - flexible, friendly and stress-free. IBM is a big brand. They hire a lot - even during recession.
Cons
IBM is a big brand ONLY for its clients/partners. Based on its brand value it would be foolish to judge IBM as Best Employer. It is in fact a very average employer. Employees (I can speak of Indian counterparts) are poorly paid, no hikes, sham appraisals, minimal career growth, minimal career opportunities, poor onsites. Most of the Indian projects are maintenance based. Even though they hire a lot, they fire a lot too. Also the attrition is high. But their business model still works for them. Because their business doesn't get affected at all if an employee leaves the org - IBM replaces him with another "bakra". For IBM employee in a project just adds up to the headcount that can be billed to the client. His knowledge is never a critical factor for the project. However, there are few employees I know who have got lucky here and are getting good benefits. Overall, if you are NOT amongst the few lucky ones, you will end up in a big account with horrid time ahead!