Use it as a training ground and leave for better sights.
Pros
I have been working for IBM (PWC then BIS/BCS and now GBS) for over 10 years in 3 continents. 1. Truly global: Many opportunities to work/interact with people from all over the globe. Many opportunities to relocate and be part of global/international projects. 2. Great people: Lots of diverse, bright and interesting individuals that help build a vast network of professionals. 3. Learning opportunities: there is a wealth of material, SME networks, etc you can tap into, if you are entirely independent and willing to put in the effort. 4. Big Machine: when you understand how the system works, you can use it to accomplish things that would be very difficult to do in other companies. 5. Secure: Once you have been hired as a non-exec and have passed probation and if you work outside the US, chances of getting fired are ultra slim.
Cons
1. Overworked: My life changed when I reached the Senior Manager and then Associate Partner levels. The hours are ridiculous and sometimes unbearable (and I am excellent at time management...). Hours are similar to MBB with half the income, more than other near-ivy consultancies with more or less equal pay and more than most IT firms less the decent bonus (even TCS and the like). 2. Too many layers: Many people are hiding in the machine with fluffy roles (that often start with "Global" and end with "Lead") and ambiguous targets. 3. Big Machine: Almost everything takes longer than it should due to the sheer number of inconsistent processes. 4. Long-term strategy: Either there is none or even Partners don't know what it is. 5. Leadership: the Leadership training is obsolete and fosters cookie cutter middle-managers. It is hard to be supportive of some leadership messages coming from HQ. 6. Pay: Behind market value in most cases, especially considering the Investment Banker's hours...