Pros
not a lot of fond memories of the experience. however it will teach you a lot about business processes and they have most every process ironed out with a book written about it. It may be a pain to work within their confines at times, but there is usually not a lot of questions about "what to do" in a situation, high pressure or otherwise, once you understand the processes.
Cons
was hired as a contractor through a contracting company. got a pay cut 6 weeks in. IBM constantly loved to save money when the contract we were working got in trouble by furloughing contractors and employees. They would go through R.I.F. (reduction in force) cycles twice a year like clock work and refused to back fill positions for long periods of time. We also got word from visiting corporate employees they loved to outsource to other countries any time they could get away with it, and were trying to convince the contract customer to allow it despite the fact it was a state govt contract. After 3 1/2 years our contract changed and moved away from IBM. Right before the change where IBM was kicked out by the customer I was the only person in my department working my shift, which prevented me from trying to transfer departments for a promotion (or at least was a contributing factor). They had stripped down labor to the point there was no backup coverage for various departments on a 24x7 contract. The contract customer was not happy either as IBM fell way behind on the contract deadlines and the customer kicked them out and replaced them.