Pros
I've worked with Cognizant for about 5yrs now, growing in the ranks and taking over a Business Development role. Some of the positives of working in Cognizant include - great brand value and organizational growth story - good career track for MBAs (as compared Infosys, TCS, Wipro etc) - fairly open work culture among peers (not senior mgmt.) - good organizational resources for self learning - good work-life balance (depends on how aggressive one is)
Cons
Here are some of the shortcomings - onsite team is too dispersed and there are minimal opportunities to collaborate - IT consulting work is minimal, though not zero - growth is tied to how sycophantic you are with your superiors - management takes advantage of employee's situation and deals out bad compensation packages (eg, visa restrictions) - appraisal process is quite a joke. If you don't make enough noise in the organization, you can never get promoted, irrespective of how good your performance has been